well..it could be a broken or missing compressor spring or rubber/isolator mount ( there should be one under each corner of the compressor where it mounts to the bottom plate.)

or it could be a broken internal snubber spring inside the compressor itself, these act like shock absorbers for the small piston pump inside the compressors housing, to absorb the torque (tendency to twist opposite of the motors rotation) of the electric motor that drives the compressor (internally) on startup & shut-down of the compressor.

if it is a broken internal snubber spring, the compressor may sooner or later break the internal tubing connecting the copper lines to the compressor/pump itself, & then you'll have a unit that will run , but it won't cool because it will be unable to circulate the freon.