Re: Bosch motor noise
This could possibly be “bearing chatter” or “screech”…caused by dry,worn bearings ,the armature enters a resonant vibration phase….you are unlikely to do “serious”damage ,as it’ has already been done!
(normal wear and tear! )
However, if you ignore it, it will get worse and the bearings will collapse or sieze-up
If your skills stretch to it, strip the motor, wash the (ballrace) bearings in petrol, pack 1/4 of the space with general-purpose HMP grease such as Castrol LM. (bearings may be shielded)
It may be possible to use a hypodermic syringe, with a large needle, to inject a bit into the bearings without the stripdown.
Not an ideal solution, but better than ignoring it!….motors are expensive!.
(new bearings are relatively cheap and almost invariably they bear a generic universal size/type code )
I assumed you have checked the motor-brushes and eliminated drum-bearings, also the drain-pump from your list !!!!
UNPLUG BEFORE INVESTIGATING! Often, the NEUTRAL is switched,meaning LIVE components,even when switched off.
As you say, hard to diagnose over the net!