You can try adding lubricant to the system to see if doing so quiets down the compressor. It is possible for these things to lose oil out the compressor front seal while (pretty much) retaining the refrigerant charge. I lost a 10P15c this way...

A good shop can add oil without discharging the system. They will have a special tool which holds an ounce or two of oil. Fresh refrigerant is then used to push the oil into the system. If this quiets things down, you've found a new lease on life... Have them inspect the system for signs of oil loss. A front seal leak will dribble oil out the bottom of the compressor pulley and back along the body of the compressor.

Be certain the correct oil is added. If you are still running R12, then mineral oil is correct. If converted to R134a, then you have either PAG or POE. These two don't play nice together, so you need to determine which you have and add only the same.