I recently purchased a 2008 tC and the car has begun a strange noise from the rear left wheel. It only happens when I am using the brakes and coming to a stop. I can only hear it at slow speeds (below 20 mph). It does not always happen but seems to after driving around for a bit. It also seems to be getting progressively worse. I made an appointment with the dealer but was wondering if anyone had any idea what was wrong. They put on new front brakes and resurfaced the rotors when I bought the car and would be really surprised if I just needed new rear brakes as the dealer probably would of caught that.

Video of the noise:

 

sounds like your brake caliper possibly binding. Do you notice that the noise changes with how much pressure you put on the brake pedal? If you do, it might be that the sliding pins need to be re-lubed. That binding could be what you're hearing.

I see that there weren't any weird bumps in the road, so it don't see how it would be shocks or springs. can't see it would be bushings, since you're not flexing only stopping slowly.. well that's my 2 cents.