noisy relay

Solid state relay! Totally noise free. The mechanical relay on my air compressor used to clang and make me jump, so I put in an SSR. The first one was too small, and fried. Then I got a 480 V 50 A unit, and it has been handling severe air compressor service for nearly 10 years, now. (You'll need some kind of control transformer and rectifier or something to drive the input signal.

Jon

you don't need to change coil voltages. Others have provided good info. here is some more background

the buzz is because your AC current goes through zero 120 times per second, and so if the actuator is not fully retracted, the spring will lift it a bit - it is exactly the design of a buzzer. An AC relay coil has an extra small copper winding to help this but the buzz is not fully eliminated, and as you have discovered, it can be pronounced. Going to DC eliminates the passage through zero, but only if you add a filter capacitor also - if you use a 120V coil, pretty much any motor start or run capacitor will do the trick (I'm picking parts you may have lying around). If you are worried about current limiting, add a series light bulb whose current is near the coil current (light bulbs, conveniently, are kinda sorta constant current devices over their useful operating range) - 100 watts per amp aproximately

I'm told SCRs fail closed, something to think about...

Check the mounting specs on that relay .. .. some are to be mounted in a certain orientation, vertical, horizontal, etc. Possibly weakening the spring which opens the contacts after coil current is off will eliminate your problem.... coil trying to pull the armature UPHILL against a sturdy spring can cause chatter. HTH Ken.