When my central air compressor kicks on it makes a loud vibrating noise that can be heard and felt in my second floor bedroom.After it kicks in it works and sounds fine .What could be causeing this loud vibrating sound

If you have a garbage disposal, look inside it with a flashlight. See the three or so teeth that grind the food up? That's kind of what it looks like inside of a compressor. Over time, the "teeth" get loose, and since they go in a circular motion when on, they get loose, and make a loud and obnoxious noise.

This is an indication that it is on it's way out. It can work for the next several years, or the next several weeks then quit.

The only thing you can really do to keep it as quiet as possible is to place some kind of shim under the condenser itself. BE CAREFUL AND GENTLE when doing this, because you do NOT want to kink the lines.

XenoSapien

If you have a garbage disposal, look inside it with a flashlight. See the three or so teeth that grind the food up? That's kind of what it looks like inside of a compressor. Over time, the "teeth" get loose, and since they go in a circular motion when on, they get loose, and make a loud and obnoxious noise.

This is an indication that it is on it's way out. It can work for the next several years, or the next several weeks then quit.

The only thing you can really do to keep it as quiet as possible is to place some kind of shim under the condensor itself. BE CAREFUL AND GENTLE when doing this, because you do NOT want to kink the lines.

XenoSapien
I forgot to indicate that there wasn't any noise or vibration until a service person said we needed freon and put it in .then the problems began.It may be a coincidence which is what the company says.What is your feeling

Probably nothing the tech did. Look at the bottom of the compressor. You should see 3 mounting bolts with rubber bushings. Are all the bushings OK? You can tighten the mounting bolts a little, just don't overtighten. See if this dosen't help. Good Luck