Compressor sick.....

When my compressor kicks in, it makes a sound kind of like a drum roll. I only get the noise when the AC is on. I'm no expert, but could my bearings be going? Is there a way to grease them? I've had the belt tension checked, but could it be to tight? Could loosening the belt help or has the damage been done?
Thanks in advance

I had a 1992 that used to have SIGNIFICANT compressor "rumble". I checked compressor pressures and temperatures, and everything was normal. I changed belts, too. Nothing seemed to get rid of the rumble, and I learned to live with it. In spite of that annoying noise, it worked well here in Phoenix (where we used our AC about 8 months out of the year) for several years.