Misalignment: misalignment may cause two time RPM vibration. This is corrected by re-aligning the compressor shaft one to another.
Unbalance: unbalance in the compressor shaft may cause one time RPM vibration. This is corrected by balancing the compressor shaft on a balancing wheel.
Overhauling: multiple RPM vibration is symptom of damaged bearings. This is corrected by a total overhaul of the compressor or replacement of parts.
(The above are only a simple clue and not a standard confirmed judgment)