'So if the 50W gets rid of the problem, should I just keeping using 50W or do I need to rebuild the bottom end maybe?' No, if it helps it just shows you that its internal engine and will need repair. 50W is really too heavy for general use, but on the other hand if you only start the mower in hot weather it could buy you a little time (but maybe not, as bigal says). Let's put it this way - if you had to ask the question, we already know you're not an experienced mechanic, so there's no way you can overhaul the engine yourself. It also would not be cost-effective to have a shop do it. The best thing is to buy a new or good used engine or mower. It depends on the condition of the deck and drive system. One last thing to check is the engine mounting bolts (to the deck). Make sure the engine is not moving. One more; Take out the spark plug, turn the mower up on its side with the carburetor side up and spin the blade to make sure its not hitting the deck. Check for a bent or broken blade. Balance or replace the blade to see if the noise is related to the blade being out of balance.

***Noise indicates a problem?*** Not "really". The noise in itself is not a problem, but it could indicate that there is some kind of problem. Though noise reduction is one of the aims in the hydraulic lifter concept, they seem to have a tendency to produce noise unique to themselves in some cases. The most important benefit of hydraulic lifters is the fact that they allow the valve train to safely operate WITHOUT ANY VALVE LASH (clearance), and reduce the frequency of checking and adjusting the valves. Engines that use solid lifters (tappets) must always have a specified clearance, or "looseness" in their valve train. If no lash is present with solid lifters, severe engine damage may be caused (eventual complete destruction is possible). *** Solution? Even though hydraulic lifters are "somewhat self compensating" (I will not say "self adjusting") for wear and stretch of components in the valve train, they still require "an initial adjustment or setting, during assembly. Given that initial setting of hydraulic lifters is not as critical as the same procedure for solids lifters, and the quick pace of the modern assembly line, it is possible that one of the lifters in your engine received an inadequate "tightening" and is operating near its "extended limit". Also, because some engines with hydraulic lifters use just a "self locking" adjuster screw (instead of a screw & jam nut as with most solid lifters), one of the adjuster screws might have "backed off" a bit. **** And perhaps an explanation as to why it goes away (eventually) when things warm up?**** A few reasons for this, and the reasons may all be present.......or not. Referring back to the possibility that a lifter might be operating near the end of its "extended limit". The usual (and correct) initial adjustment for hydraulic lifters will remove all clearance (lash, looseness) from the valve train, and add a specified amount of "preload" to the lifter "center plunger" or cylinder. If the initial adjustment resulted in less than "specified preload", the lifter may be allowing a bit of clearance to develop (and noise) until ALL the valve train components expand (when hot) and eliminate that lash. A loose locking adjuster screw that has "backed off" would do that too. Another typical reason that hydraulic lifters become noisy is related to how the lifters "recharge" with oil during normal engine operation. In the Kohler "demo" of hydraulic lifters (see link in previous post), it is stated that the lifters "draw" oil. Not really "draw oil" as if the lifter was "sucking up oil", but to "fill with oil" being furnished by the engine lube oil pump. Because the lifters are "fed" by the same common oil galley that supplies oil to all the other "pressure lubed" components in the engine, the lifters receive only "a share" of the oil, not the entire flow. As engines get older, they begin to show some wear in all components. Wear to the crankshaft main and rod journals and bearings, wear to the camshaft and its bearings, and wear to lifters and the bores that they operate in. All this wear has a cumulative or, additive effect that can result in "increased internal leakage" of oil in the oil galley network. In the layout of "who gets what" in regard to oil distribution in an engine, the lifters are usually at, or near the "end of the line". So you could say that the lifters are fed last, with least oil pressure. This condition is apparent at cold temperatures (because cold oil doesn't flow well) and at idle (because a slow spinning pump moves little oil). When the engine is cold, the engine is "leakier" inside because the parts are contracted---more clearance---more leakage---less oil to the lifters. Consequently, the lifters don't get "fully charged" with oil in the short period that they have to "take on oil". As the engine warms up, the clearances shrink somewhat, and leakage decreases a bit. As the oil itself warms up, it flows more easily, so the lifters get a better charge of oil and usually become quiet as they reach "zero lash". But an old engine still has more looseness than when new, and because warm engine oil flows easier, the internal leakage also is more when oil is warm. In the engine, the oil pump experiences the least wear of all spinning or moving parts. For this reason, the oil pump is usually capable of maintaining adequate oil pressure to overcome all the leakage and other variables. To make sure you DO NOT have a real problem, it would not hurt to have the valves checked to see that the adjuster screws are secure and that the adjustment (initial adjustment) is correct. It will have to be done correctly (by the book) and if you aren't capable of that, or equipped to do......best leave it to a good shop. DO NOT simply go in and start tightening adjuster screws. It must be done properly.

Okay, this is much later from the original post, but I just want to address this issue. Having been in one unit for years and experiencing those who have been quieter and more normal walkers than others, some are not. Currently, there is the loudest, hardest heel-striker living above, usually driving me nuts for hours. My ceiling CRACKS and SNAPS with each thudding footfall...(and is mostly carpet). Like any repetitive sound that intrudes another's space, this becomes too annoying. I have shared a recording of this noise with others and they are aghast at how it sounds. (The manager thought it was something else, when I showed her, trying to make my point). When this comes up, many will bring up the structural aspects, some saying "It's just the building" in defense, while they walk like fools. The assumption in these cases is that the flooring needs repair, when the problem is the aggressive walker. (Of course, this is always seen as being brushed over since "how one walks cannot be controlled", is "everyday living".. yada, yada.. yet is such an issue I've seen discussed often). I wanted to bring up, since when discussing with some lately, they typically assumed the construction here is failing, but was not this way prior. Today I was aware that he's had a visitor up there all day while he was gone and noticed that that person was not disruptive at all, walking normally, proving to me that the floor up there is still fine after all and that it is only due to big foot making rushed, thudding long strides on my ceiling. Ho-hum. As the offender arrived, I am becoming tense. When he walks over the area where I am sitting, I can feel a dizzying sensation, like my couch actually shifts, apparently due to everything being connected. What occurs often is this endless walking around...like there's "so much to do", rushing back and forth.. back and forth. Anyway, I feel that one who walks with reckless abandon just should NOT live above another unit. If anyone has ever indicated to one like this that they walk hard, they should STOP... think....and NOT rent above another. It will save everyone involved a lot of trouble. (That goes for the person being regularly caffeinated, or hyperactive, having ADHD or something). Though I know that many do not realistically function by being self-aware and sparing others, it would prevent such problems). This is what I am going through, possibly getting another unit here, which I don't even want to do (and can't be upstairs), while waiting for certain housing elsewhere, since I cannot stand being invaded each and every day by this. So, I feel the need to have a stressful move just due to another's habits, yet this could just be avoided if one like this would just live in a lower unit! (Though others would still have to hear his constant sound system and BASS noise, the other issue), furthering the thought that one like that should live in a private home if refusing to make adjustments.

Thanks, everyone! @homepro01 - the dishwasher is a KitchenAid Model #KUDI01TJWH0. Nothing (that I know of) has changed with respect to our plumbing. @antss and weedmeister - I spent some time the other evening and take apart as much as I could :-). I took the bottom sprayers, the filter looking gadget :-), and got as far as the what I'm seeing is called the "chopper assembly" (pic here http://www.partselect.com/PartDetail.aspx?Inventory=392939&SourceCode=1). I didn't find anything hard like glass or metal. Everything was mushy and soft. Should I go further? Also - not sure if this was a bad idea, but with all the parts all the way to the chopper assembly taken out, I started a rinse cycle, let the water fill for a few seconds, then canceled the cycle to drain the water. The noise was still there. So I'm thinking whatever is causing it is further down in the system. Should I keep going all the way to the pump itself? And is the pump accessible from the top? Or from underneath the unit?