I rent an apartment that is heated/air conditioned by a Mitsubishi wall mounted unit with two pumps installed on the outside wall of my bedroom. Last year, I didn't seem to recall having any problems, but since winter set in, this year, there have been periods of excessive humming noise and vibration so that I could not sleep. Then a couple of weeks ago, during a snowstorm, water came through the ceiling unit in my living room. It ceased rather quickly once I shut down the unit. Interestingly enough, the outside noise and vibration seemed to have quietened down until a week or so ago. My landlord checked and confirmed that he heard the noise outside my window, and called a service technician, who came today. Low and behold, nice and quiet, no issues. I told him it was intermittent, but the company doesn't really deal with Mitsubishi so the representative couldn't offer an explanation, just suggested to tape record it when the noise happens again. I am not crazy or oversensitive. As a matter of fact, I have severe hearing impairment in one ear and cannot hear the alarm go off if I am lying on that side. Yet, for nights and days and weeks, the noise and vibration was so intense I couldn't sleep or concentrate on any activity. Has anyone else had this problem?

Thank you for the replies. I’ve been off on a cub scout campout so have been out of pocket. I will try and answer the questions. The unit that is failing is a 4 ton R22 unit – model SSX160591AA It was installed in 2012, with no indication that a new coil was installed at the same time. There was also installed at the same time a separate 3 ton unit R22 unit – model GSC130301EB. Together these units cool the first floor of the house. So it seems like in 2012 the prior owner chose to replace the condensers only, and had to do it with R22 units to avoid replacing the coils? Which is a little strange because one year earlier, in 2011 a new unit was installed for the upstairs. It is a 5 ton R410a unit – model ssx160591aa . The receipt shows a new coil was installed at the same time. All these units support individual air handlers (three of them). For heat there is a boiler that circulates hot water to the air handlers. Last year I had a lot of ductwork work performed – the HVAC company I worked with says the system does not have enough air intake capabilities, so they vastly expanded all that. It made a noticeable difference. They also reconstructed the upstairs ducting so that there is a return path for the heated/cooled air (it is a dual zone system and did not have a return path). I liked the work they did, but I also worry that it was their work that led to the premature looming death of the compressor. They had the coils and air handlers out to redo the ducting. Thank you for providing answers and perspective. I just ordered a big book from Amazon on HVAC to try and educate myself a bit. Any recommendations of books or websites is appreciated.

That condensate pipe is for your AC, not your furnace. I doubt you are running your AC right now, it's cold most places right now. Because you have a gas furnace it's unlikely your AC is a heat pump. So the noise you are hearing is probably more related to plumbing than HVAC system. The thumping and tapping may be coming from water heater. If it is cold where you are and you haven't been running the AC I would get a plumber to investigate your water heater and plumbing system. There looks to be a water shut off valve toward the top of the picture you posted. What does that go to? It could be water hammer noise from the condo being renovated. Maybe they subbed out plumbing to a general contractor and he made a mistake?

To answer your question this is not normal. Are your renting this property? If so then your maintenance guy does not want to be bothered or spend the money to fix the problem. It sounds like the mechanism which changes the angle of the vanes is rattling. Some mini splits are able to oscillate the position of the vanes in order to help distribute the air. You may be able to turn off the oscillation with the remote control. Here is a video for the Mitsubishi remote control. Your unit may say Trane on it but I believe it is made by Mitsubishi. If this is not your remote then a model number or photo of the remote would help determine what you have.