What kind of conveyor? (screw, belt, bucket, etc). What material is it conveying? How long/high is it? How is it driven (gearbox, belts, direct drive, etc)?
From the conveyors I have seen, noise/vibrations are often caused by overloading, improper alignment of the rollers/bearing assemblies, worn bearings, and improper lubrication. I would hazard a guess that you will find a mechanical or operational problem rather than electrical.