Need help diagnosing popping sound

[TWO STEP TEX]

Hello everyone, thanks for taking a look. I apologize if this is in the wrong spot. I just bought a 84k mile 2011 135i with DCT. When I get into boost and let off I get this popping sound, I can feel it as if it's under my seat. Took it to a shop and they said they couldn't re create it (I don't think they drove it hard enough). I'm not sure if it's suspension related, driveline mount related, or dct related. Feels like a rock is bouncing off the underside of the car. Anyone else seen this before?

[Petro135]

Originally Posted by TWO STEP TEX

Hello everyone, thanks for taking a look. I apologize if this is in the wrong spot. I just bought a 84k mile 2011 135i with DCT. When I get into boost and let off I get this popping sound, I can feel it as if it's under my seat. Took it to a shop and they said they couldn't re create it (I don't think they drove it hard enough). I'm not sure if it's suspension related, driveline mount related, or dct related. Feels like a rock is bouncing off the underside of the car. Anyone else seen this before?

I'd say loose belly pan but if only when letting off boost I doubt it. I had the transmission part of the belly pan loose and it sounded like someone was banging on the bottom of my car when ever I got to like 45 mph. You best go under the car and shake everything around and see if anything is loose first before you spend money fixing something that is not wrong with it

[TWO STEP TEX]

Originally Posted by Petro135

I'd say loose belly pan but if only when letting off boost I doubt it. I had the transmission part of the belly pan loose and it sounded like someone was banging on the bottom of my car when ever I got to like 45 mph. You best go under the car and shake everything around and see if anything is loose first before you spend money fixing something that is not wrong with it

Ok thanks for the advice. Haven't had a chance to get under it, the struggle is real in NYC without a garage. I was shocked that the BMW specialist shop I took it to couldn't find anything causing the noise or re create the pop. I plan on changing DCT fluid before winter hits an will try to pinpoint it myself.

[TWO STEP TEX]

UPDATE: Finally had a chance to get under the car. I discovered that the driver's side motor mount is missing 2 bolts and the passenger side appears to have 2 bolts currently backing out. I'm kinda pissed because I took it to a shop in Queens that "specializes" in BMW and asked them specifically to check the motor and driveline mounts. They told me everything was in excellent condition, couldn't replicate the pop and then charged me 250.00. Will report back after repair.

[TWO STEP TEX]

Ok, so I was able to get one bolt in the driver's side and then torqued down the passenger side bolts. After a test drive, I can 100% confirm the popping was the motor mount. Now to figure out a way to get the other bolt in. Might have to get an engine hoist or just take it to a shop.