It should turn around smoothly, without any 'hickups' (be sure to completely shut down the air compressor!). Check the isolation of the motor windings. Should be in the mage-ohms (you need an isolation tester / high voltage ohm meter for this). Check the voltage when the compressor is running.
[pdf] Loose screws, bolts, or other components can vibrate and create noise during operation. Tightening these components can often resolve the issue. 2. Worn Bearings Bearings wear out over time, causing friction and noise. Replacing worn bearings can restore quiet operation. 3. Intake Air Filter Clogged
[pdf] Generally, of the two air compressor types available for hire, rental rates for portable models range from $45-$90/day or $100-$200/week. In contrast, a trailer-mounted compressor rental costs $75-$950/day or $220-$2,500/week.
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