Hi GTN, Very good question. I'll bet your 3/4" spigot has a 1/2" copper line feeding it nor is a spigot 3/4" through out it's length. Smaller to bigger or vice versa doesn't matter. Size affects velocity at that change point, but very briefly. Length of pipe is what affects the system efficiency (loss of pressure) the most. Water flows faster through the smaller diameter pipe and when water velocity gets high enough turbulence in the pipe is reached and your friction loss per foot of pipe increases as well as noise. This friction loss robs you of pressure as the water travel along the system. Your system has high pressure so this not a big concern in your system. It becomes a design issue depending on where you reduce your pressure for your garden. 1 1/4" pipe was sized by a formula that calculates flow versus velocities in various size pipe. A standard design criteria for non-turbulent flow is less than 5 feet per second velocity(noise reduction). Using that criteria the 1 1/4" was acceptable, 3/4" would be less acceptable but still can be utilized with no real problems. It then becomes a cost issue. It makes no difference what size the source pipe is, but hooking up to your house affects the velocity of water traveling through your house pipes. If you turn on your hose, how noisy is the flow in your house? Does it affect the flow of other water using appliances being used at the same time? Turn on the washer, shower, kitchen faucet, etc an listen to the sounds of the water. If the answer is no to these questions your house water system doesn't pose a constriction to your garden water needs. The more items being run the noisier it gets. Did you ever call your builder and find out about the pressure regulator needed for your house water system? Just curious. GL. Aloha

I'll assume that you can't see any particularly wet spots. That said, if the leak is in one location and you've dumped many gallons of water at that spot, try a prod rod. In most soils, excluding very sandy ones, the drier the soil, the more difficult it is to insert a rod (or screw driver) into it. a saturated soil can be easily distinguished from drier soils by the relatively great ease in pushing a rod into it. If you know where your lines are, follow them with the rod looking for the very soft spot. If the leak has been happening for a long time you will probably be able to put the rod in the ground easily for 1-4' or more. My prod rod is a piece of steel bar stock 4' long x 3/8" dia. with a 1/2" ball bearing welded to the soil end and a T handle on the other. The ball bearing is there to help keep me from shoving the rod through pipe, definitely a no, no! If you are looking for a leak in pipe only a foot or so deep and know where the pipe is it should be very easy to find the leak. Sometimes it can be useful to look for differences in what is growing on the ground as plants respond to vastly different moisture levels, like cattails sprouting in a cactus garden or just more growth in a small spot. If you want to spend thousands of dollars, there are devices that are made to do just what you need that hook onto the pipe and work very well down to depths of many feet. After you find your leak maybe you could start a small business hiring out to find leaks for others and get rich :)

The first thing that I would try is to turn the valves on manually using the manual screw at the valves. This would be to see it there is water in the system. I am confused about the "main valve" . I have not seen a main valve that is a solenoid valve connected to a clock.

Thank you all! @nikness30 got it right on the nose. Looks like it's something called a "Chimney ballon"--and water must be leaking from the chimney, and the noise must the water pinging on the bag. It's weird--I had to zoom in for this picture--I can't come close to reaching that tube you use to inflate it. Oh well, tomorrow I'll inspect the chimney from the roof. Thanks again!