Weird brake problem on 05

Okay, so my "new" car that I just got, with less than 4,000 miles on it, has a weird problem. When you're waiting at a stoplight and slowly ease up on the brake pedal, the car "vibrates" slightly as though the calipers are locking up. The moment you take your foot off the brake pedal and accelerate, however, the problem goes away. It's annoying in stop-and-go traffic. Does anyone else's car do this? I took it to the dealer today, they checked the brakes & resurfaced one or more of the rotors, but they said the problem is still there.

They're going to keep checking the car tomorrow, but I suspect that maybe it isn't the brakes, maybe something else is causing the car to vibrate a little. Engine runs perfectly, so my suspicion is that maybe the drive shaft is out of balance, or maybe the automatic transmission isn't catching properly. I checked through all the TSBs and the only thing that comes close is that steering problem one, which isn't it at all.