[yokai24k]

TLDR: 2-3 knock & pop noise coming from outside of the cabin whenever I take my foot off the accelerator too fast. Sounds like its coming from under the front half of the car. Can someone help give me some insight? Would be much appreciated, thanks in advance!


I just bought a 2019 330xi (executive demo) from a BMW dealership a few days ago. I was driving with my windows down and noticed a couple knock and pop noises coming from outside of the car when I would take my foot off of the accelerator too quickly. When I put the car into eco pro, it barely made that noise. When I put it into sport, it pops and knocks more frequently. However, regardless of how fast I take my foot off of the gas, when I'm in stop and go traffic it happens almost every time. Not sure where the noise is coming from, but it definitely outside of the cabin.

It doesn't sound good at all and my dealership/sales rep isn't taking it too seriously. I want to take it in ASAP because it doesn't sound good at all. During the test drive, I was driving the exact same way that I'm currently driving the car and I didn't hear any of these noises (even when I was in sport mode).

I've searched through forums on here for the past few days and can't really find anything that exactly explains what is going on. People were saying that it sounds like either a fuel injector issue, cv joint issue, gearbox mount/transmission issue, or a valve flap opening in the exhaust system. Someone said that this is a normal sound for the car, but I really hope it's not.

Not too savvy with engine mechanics so bear with me. After doing some research online, I'm starting to think it might be pre ignition, detonation knocks, or transmission issue. My reasoning behind that is because it only happens when I'm taking my foot off of the accelerator, and because the car sometimes feels a little weak when this happens (almost like it's burning up gas too quickly inside of the engine).

Can someone help give me some insight? Would be much appreciated! Hopefully this is enough information, I'll def provide more if needed. Thanks in advance!