My rebuilt Bosche has a high-pitched whistle, particularly at low RPM.
I disconnected the wires, and the whistle stops completely - so it's
not mechanical. It turns smooth and functions fine.
I installed the unit 2 years ago, and I thought the whistle would go away after the brushes broke in. But now it's starting to bug me.
Any suggestions, rather than get another unit?
maybe replace the regulator? Maybe replace the capacitor on the housing?

Tks,
DG