WWTBAM Bored

So I think I'm having some issues with my brakes. They stop the car as they should, but they're making a weird thumping noise.

The backstory: we were gone for about two weeks. While away, two big ice/snow storms apparently hit our area. When we returned to Green Car in the lot at the airport, there was a thumping noise when the brakes were applied. Everything looked ok, so we figured it must be some ice accumulated somewhere under the car. Probably true, as Green Car stopped thumping before we were even on the highway home.

The next day, we were out and about in town in Black Car. Same thumping noise that Green Car had made, so we assumed it was the same thing. Only Black Car's thumping never abated, but no time to check it out just yet. We left town again for another 6 days, and returned to find that Black Car is still making the thumping noise whenever the brake is applied.

So the thumping noises were identical, but obviously they must be from very different sources. Any thoughts as to what it may be? They are ABS brakes, and I'm not sure when they were last serviced (NN's car). This doesn't seem like an urgent problem, but NN is out of town until the 31st and I don't want to drive unnecessarily if it means that my brakes are about to crack up and fall off!

I'm notr a mechanice, nor do I play one on the radio, but here's a quick google pass:

http://tinyurl.com/2fcnva

http://www.2carpros.com/topics/brakes1.htm

http://tinyurl.com/yokzzc

Is the thumping at a constant rate or does it slow and finally stop when the vehicle slows down and stops? If the latter, you probably have a warped rotor or a broken pad.

An ice storm isn't going to magically warp your rotors for you, but if they're already warped I supposed all that gunk might help exagerate the effect.

I vote for "stuck caliper". For some reason there is a caliper-equivalent-part even with disc brakes. Moves the discs in & out or whatever. I think not just with the emergency brake, though it certainly does operate that way, or squeezes the rim from both sides like a bike caliper? I have definitely had this thing freeze on one side in an ice storm, leading, of course, to needing an entire brake job (including having the now-warped rotors machined back to specs, or replaced) all around when I got where I was going. Even though I'd recently had one. I don't drive my old car in ice storms or very far (over 200 miles away) in any weather any more.