Smith837

Just tried to back my 2021 S4 out of the garage. I checked to make sure the parking brake was released, put the car in reverse, and lifted my foot off the brake, but it didn’t idle backward. That was unusual. So I put the car back into park, then into reverse again (it felt like the transmission shifted into reverse), but the same thing happened—the car didn't move. Next, with the transmission in reverse, I gently tapped the accelerator to see if the car would budge. As the engine began to rev, the car suddenly lunged back and at the very same moment, I heard a very loud mechanical clunk/bang. The car shook too—i.e., it felt like I hit something (but didn’t). Any ideas on what just happened? My thoughts turn to either a stuck parking brake mechanism OR something with the gearbox. The car hadn't been driven in a few weeks, but I've never experienced anything like this before.

I tested the car after and it drove fine. No discernible issues, although I initially heard a gentle repetitive “tapping” noise coming from the right/rear of the vehicle when applying mild brake pressure and bringing the car to a stop. That noise faded/disappeared after driving a bit. Drove the car to my dealer about 30 minutes away. Nothing unusual during the drive. The car is at the dealer now for service, but I haven't heard anything back from the techs yet. Appreciate any input.

A4Audi4Fun

Might have been severe rust buildup in the pad / rotor area or the mechanism that releases the brake. Tapping noise suggest more likely rust on the rotor though that got cleaned up after a few brake applications.

Aviator6

Yeah, especially if rotors were wet when you last parked, or just some very high humidity. I've learned not to garage my car just after washing it - take it for a short drive to dry the brakes. If it is raining when I pull in the garage, I make sure to not let the car set for any longer than necessary before driving to clean the surface rust from the rotors.

Smith837

Yes, I suspect some build up. The dealer said that what I described is quite common. They looked at the vehicle (and will test drive it), but sounded like nothing to worry about. Appreciate your input!

Smith837

As a matter of fact, I rinsed some crap off the car a week or two prior, and promptly put in the garage without a quick drive first. It then sat there for a week or two—so it's very likely I did this to myself, so to speak. Won't happen again though.

Thanks for sharing your perspective!