Noisy compressor

Last week I bought a 20 gallon compressor for next to nothing because it wasn't building pressure.  I took the head off and cleaned the valves, replaced the o-rings, and it's good as new.  The only problem is that it's loud.  I would love to make it quiet if I can.  Any suggestions would be appreciated.https://bid.comasmontgomery.com/lot-details/index/catalog/24332/lot/3638998#mz-expanded-view-1194594785468

An air filter on that rectangular plastic part will help a little. Or see if it unscrews and find a compressor intake filter. If it is an oil less compressor they are just loud no matter what.

Put it in a box? I'm bou;ing an "outhouse" outside the barn for the 4 horse 80 gallon I have

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Direct drive compressors are loud. The only thing that shuts them up is distance and walls. Put it outside in a outhouse or put it in a box. If you go the box route make sure it gets some cooling air.

First, start by installing an air filter on it. Having it wide open like that is making it worse.

Quite often they are National Pipe Thread and you can use nipples and elbows to get creative with big air filters. McMaster and the like even sell sound attenuating filters for air compressors.