I noticed my cameron micro drill press was acting funny after being unused
for a while. It's paired with a fairly new model 2A speed controller. The
problem was the motor would start to race for fractions of a second at low
speeds. It would sometimes make stuttering sounds several times per
second, even at no load, but only at low speeds.

Medium to high speeds were fine, and running it didn't help at all. The
brushes looked fine.

I gave them a call about this and they said, yeah, we know about this
problem. Some model 2A controllers were made with a bridge rectifier after
the speed controller, which was supposed to reduce brush wear for 220volt
market customers. For others, this caused the weird racing and stuttering
effect. They said just remove the bridge rectifier or short it out and
you'll be fine.

I did that today by just removing it to use somewhere else and things are
OK again. So yeah, that's the official fix and it works fine.