For those of you that have noisy roof a/c I have found a remedy! maybe this has been mentioned before but I have not seen it.
Dometic makes a SVC grommet kit that includes foam pads, anti vibration campers, and compressor grommets to get rid of the awful loud vibration.
I ordered mine from Dyer RV in Phoenix for about $17.00 and shipping charges. Now I don't have to turn my tv volume up when the a/c compressor kicks on, and back down when it shuts off.
I was almost ready to replace the whole darn unit.
You can order from their website: dyersrv.com!