Here is the deal. After braking (soft or hard) when I release the brake pedal then accelerate, you can hear the brake booster diaphragm "pop" back to neutral. After releasing the brake, the brake pedal returns instantly to the standby (non-depressed position) but the booster goes on a few seconds later to sound like a damper door shutting. I took it in and the techs (along with help from the engineer help line) diagnosed it as a harmless sound that is a by-product of the design. They said they tested another '09 on the lot (new) and it did the same thing. If it did it everytime, I might buy it, but it is intermittent. Anyone else out there had something similar? I am at a dead end (at least with this dealership)
I do believe I have experienced the same noise you are experiencing and it does sound very similar to a damper noise as you described, but it can be loud at times. I have learned how to avoid the issue by altering my driving habits and only rarely hear it because of the change.
"Yes, I was having the exact same problem as you were. Called a friend who a mechanic. He explained to me that the only thing probably happening was the lack of, or too much "air" in the vacuum braking system. He instructed me to turn off the vehicle, pump the brakes until it won't pump any more (about 3 or 4 pumps), and that should eliminate the air, or gaps in the vacuum system. It actually worked. Once I did that, it didn't matter what I did acceleration wise, or how long the truck sat, the noise was gone!!! That seemed to have worked for me. He said only if it is consistent will it actually be the brake power booster, meaning every time you accelerate from braking, not just once after sitting. If it was occassionally, or after sitting, it meant that the there was a lack of, or too much air in the vacuum braking system. He said it commonly happens with temperature/pressure changes, outside, similar to what can happen with tire pressure. He said that the people who got theirs replaced thinking it was the problem, the technician would have "pumped" or bled the brakes anyway eliminating the problem after an unnecessary part change."