Noisy roof AC

Don't know if you have mud daubers in California but they can screw up an AC. There is usually a vibration with the dauber nest on the fan blade or fan shaft.
Easy to find and remove.

Get up on the roof and take the cover off. There are some baffles in there that can have loose screws etc. Also a popular place for birds to make a nest.

My rear Dometic was noisy until I changed the gasket, then it quieted down. I expect the old gasket allowed the mounting bolts to loosen. Do not over tighten the mounting bolts or you'll have a leak. They take something like 40 INCH lbs of torque.

check it to see if the mounting bolts are tight. Will be loud if not

I was able to quiet my AC considerably by removing the cover and insulating it with foam around the edges and between the input and exit of the air. Be very careful to not block any airflow. I discovered that a lot of air was traveling straight from output to the input because the separation was not sufficient. After making sure the separation was better I had a better output from my duct work..

I just recently had the original 2001 noisy pain in the butt front dometic unit changed out in our DP. We bought the RV 5 years ago but the front a/c had a loud irritating noise. It cooled well so let it go. The compressor finally quit so it had to be changed. The irritating noise is now gone but it is still loud running.Just the way it is. Mine is a ducted unit.