filtering fft spectrum further?
Processing for vibration analysis can be quite involved, depending on what type of machinery you're testing, the kind of faults you're looking for, the technique(s) you're using, and the test equipment you have available.  Without more specific information, I presume you're doing something like that described in the 'Envelope Detection' section of:

http://www.bksv.com/doc/bo0501.pdf

Since your spectrum is not clear, there could be any number of things wrong, such as: 1) improper placement of accelerometer, 2) improper synchronization, 3) improper analysis bandwidth, etc., etc., etc.  A lot of things can go wrong, and it's not an area for amateurs. No company wants their million dollar engine or generator to burn out or blow up because some technician didn't detect an impending failure.

There is an extensive field of literature, and a host of companies that train people to do vibration analysis (e.g.:

http://www.mobiusinstitute.com/site2/landing.asp?LinkID=106
http://www.mobiusinstitute.com/site2/detail.asp?LinkID=53

A brief bit of googling can easily lead to hundreds of thousands of hits, some of which may be quite specific to your machinery, measurement set-up, etc.