1
Loose mounting / failed isolators
CheckVisual; check bolts.
FixReplace isolators, torque mounts.
2
Worn bearings (motor or airend)
CheckVibration analysis, listen with stethoscope.
FixReplace bearings; airend may need rebuild.
3
Valve flutter (reciprocating)
CheckListen at head.
FixReplace valve plate.
4
Belt resonance
CheckTension check.
FixRe-tension or replace.
Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.