There is this popping noise/feeling through the brake and/or gas pedal whenever I accelerate from a stop and start to slow down. Any thoughts on what's causing it? The brake pistons releasing? If so, why?

 

If you are in sport mode and don't have a JCW it is acting as tuned. For some reason the nitwits at BMW left the pop and burble when you let up on the accelerator off the JCW. So buy an All4 S and it sounds like a Mini, buy a JCW and get the classic Toyota Carrola sound.

If you are not in sport mode you have a problem. Could be a stuck VTC, that is the widget on the cam that adjusts timing based on the tune.

 

I got a JCW, but I can't hear the pop sound, not even in sport mode. do I have to mod the intake in order to hear the pop?

 

ok to be clear it is not the exhaust popping. I've had the car for a year I know that sound. This is related to the brakes, tranny, or maybe the suspension.

 

is it a poping sound or more of a rattling sound. I just starting having a rattling sound when Im at stop sometime. and I can feel it thru my break pedal. Sometime its louder then other. sometime its not there. it appears more when I switch it to manual mode. Idk why that is. Also if release brake pedal a little, like inch the car forward. its sometime stop.