Squirrel -cage motor noisy.

Loose wires within a coil? douse with kopal varnish?

Squirrel wants out? (Well someone had to say it...)

Mike.

Some of these motors are bolted together. Tighten the bolts if you can reach them. Then, as noted, the coils can work loose from the laminations. Varnish, or thin Super Glue might work for that.

Peter Wieck Melrose Park, PA

The bearings may not be hot but they can still get noisy.

Maybe some WD40 would help.

Is it being powered by clean sine 50/60 Hz or some sort of dirty chopped/synthesised 3 phase via a converter?

I tried pouring oil down its nose, but the noise never changes. :-)))

We have no choppers. And other squirrel motors on the same power system are quiet as ever.

If it has a phase-shift capacitor, that has probably changed value and is on the way to failing. Substitute another one of as near the right value as possible and see if that stops or alters the noise. (Make sure the capacitor is discharged each time before touching it.)

My apologies, I didn't spot that you had said it was 3Ph.

It could be one phase disconnected, although that probably would make more of a hum than a buzz. Laminations could be working loose in the rotor or the windings working loose in the stator; the former will be more likely to change on load or pulsate at slip frequency.