I have 2 MP 40 QD's on my 120 and the right one, which is almost a year old, is very quiet, most would say dead silent. My left one, however, is not so quiet. Even though it is only 2 months old the left MP40 QD had always been noisy. I have played around with it's position and that will quiet it down for a bit but then it goes right back to being noisy. The other day I decided to clean it, though it was fairly clean as it's only been 2 months, and I put some more MolyKote 111 compound (what I believe it comes lubricated with) on it and that quieted it down for a bit so I decided to try a nylon washer on the ceramic shaft between it's base and the prop magnet
Unfortunately, that did not fix it.
Then, I noticed that the tabs on the prop cover (not sure of the proper term) appeared to be bent outward slightly and, at least one may have a slight crack in it. This made the prop cover fit loosely and, possibly, cause vibration
So, I decided to heat up the tab and bend it back in slightly
I reassembled the unit and put it back on the tank and it made a difference in the noise. It is still not as quiet as the right one but is is more quiet then it was with only a very slight vibration now.
Unfortunately, that did not fix it.
Then, I noticed that the tabs on the prop cover (not sure of the proper term) appeared to be bent outward slightly and, at least one may have a slight crack in it. This made the prop cover fit loosely and, possibly, cause vibration
So, I decided to heat up the tab and bend it back in slightly
I reassembled the unit and put it back on the tank and it made a difference in the noise. It is still not as quiet as the right one but is is more quiet then it was with only a very slight vibration now.