Rear brake squeaking

What's the most likely cause of a god-awful, nails-on-a-chalkboard squeak squeak squeak squeak squeak noise coming from a rear brake? It's most pronounced under light braking (which is odd...pre-pressurization of brakes during regen?) and goes away when I put it in neutral and rely on the friction brakes for a harder stop.

I did try to make a few moderate stops in N to clear off any corrosion...no dice. I just noticed it for the first time this evening. In lieu of an idea, is it particularly difficult to yank off the drum and have a look? (All of my prior cars had discs on all four wheels...fancy that.)

 

Thanks, guys. I picked up some brake cleaner and I'll get in there this weekend if the issue persists. (May as well since I have to rotate the tires, anyway.) In the mean time I happened across Hobbit's brake adjuster write-up, which has proven very useful! Based on his description I figured it might be possible that I just haven't been braking hard enough to actuate the adjusters, perhaps due in part to some corrosion or grime that resulted from my northern holiday adventure. So I did the following before leaving work:
1) Power up the car.
2) While still parked, push the brake pedal all the way to the floor and leave it there until the booster pump quits buzzing.
3) Release and fully re-apply the brake pedal several times before driving off.

The squeaking is much better than it was yesterday or this morning! It's less obtrusive and doesn't really happen unless I'm decelerating below the 8mph transition speed. So that's progress.

 

I finally had a chance to fix it today. I had tried and failed previously because I couldn't get the drums off so this time I went at it with a pair of 8mm x 1.25 bolts to pull them off. After that it was easy. Both sides looked good in terms of wear and the adjusters still looked well-greased. The pads and drums looked a little glazed so I used some 80 grit sand paper per galaxee's instructions followed by a good cleaning. I also advanced both adjusters a few clicks to get them just to the verge of contact with the drum.

The result? No more noise! And I learned a new trick which is always fun.

 

Hey, I had forgotten all about this! (Isn't digging through your old posts weird?) Your description of the noise sounds a lot like what I remember. Inspecting the rear brakes is really easy **if** you have the pair of bolts to free the drum. You can't see anything useful otherwise. What you need to do is insert the bolts into a couple of threaded holes on the drum, which press against the hub as you turn them and free the drum. Trying to pull by hand is an exercise in futility if the drums have been on for any length of time. Trust me, I tried.

Read Hobbit's write up before you try. IIRC you need to de-energize the brake system before attempting this because otherwise there is a risk of the system pressurizing when the drum isn't there to restrain the shoes, which is probably bad.