Banging noise on throttle blip (N51)

[nj128idriver]

I have a 2011 128i 6MT with the regular sport package, no other options. The car is completely stock as far as I know (it's a CPO) and according to the serial number lookup site, I have an N51. Not sure if it matters but the car was originally bought in Pennsylvania, USA.

Occasionally when blipping the throttle during a downshift I'll hear a loud banging noise from under the hood. This happens maybe one every 40 or 50 downshifts and seems to be worse when it's colder out. It's most severe from 3rd to 2nd which is the largest blip. The banging seems to happen as I lift off the gas or immediately after. It sounds as if something is hitting the hood.

Based on nothing but my gut feeling, I've narrowed it down to 3 possibilities:

- Unburned fuel popping in the exhaust
- If the engine mounts allow excessive movement, a piece of the motor could be physically hitting the hood (no idea how much clearance there is)
- A mechanical problem with VANOS or something else

Has anyone experienced anything similar before? I tried searching the web and this site but couldn't find anything like this.

[chris82]

No never had this, I'd get that checked out

[631twentyeighteye]

Perhaps a broken motor mount or a busted trans mount allowing it to move and bang around when shifting?


Yeah never heard of anything like this, id get it checked out.

[Blacksport]

Just a guess....

the dual-mass flywheel swinging open then banging shut...

[Tuxedo]

I have a N51 and everytime I took it in for service I would state the car acts like once-ish a month an engine or tran mount is worn or bad. Every time the car would checkout but about once/twice a month I look at the car and say what the hell was that. It's only for a second and goes back to operating perfect. Head scratching to describe but it feels like the car has a worn/cracked motor mount, if it was a front wheel drive I'd think the torque converter maybe going bad. The car doesn't leak but about every 75days a smell belches from the engine and a small smoke plume.

The idle and vibration issues this N51 has had and fixed by BMW with software I've concluded that the programing of the DME needs a patch/re-program for the crazy, whack-funky shift/snap/lurch/lunge intermittent WTF issue.

[Dackelone]

Broken engine/trans mount or loose subframe bolts. ?

[Xyloft]

Originally Posted by Blacksport

Just a guess....

the dual-mass flywheel swinging open then banging shut...

would that sound more like a clunk than a bang?

mine sounds more like a broken motor or trans mount. It will clunk every so often when I raise on the accelerator or sometimes when i rev match to down shift. (so when the drivetrain switches from accel to deccel or the other way).

had BMW check it twice so far... every time i take it in, and have them ride along it makes no noise at all.

[Tuxedo]

Originally Posted by Xyloft

had BMW check it twice so far... every time i take it in, and have them ride along it makes no noise at all.

I would say the odds of scheduling an appointment, pulling in and when with the SA or Tech says whats wrong? and it replicates this issue is well over 1000/1. It is to random with no data point of events to consistently show the pattern of cause and effect. First thing the SA asks is did it trip a code? no and unless my ride along was 30days no fix will ever occur probably.

I have this issue of note with Auto tran N51

[Xyloft]

Originally Posted by Tuxedo

I would say the odds of scheduling an appointment, pulling in and when with the SA or Tech says whats wrong? and it replicates this issue is well over 1000/1. It is to random with no data point of events to consistently show the pattern of cause and effect. First thing the SA asks is did it trip a code? no and unless my ride along was 30days no fix will ever occur probably.

I have this issue of note with Auto tran N51

the worst part, after my last test, the service manager was like "maybe we're not driving it hard enough. Why don't you take me out and we'll see if it does it" we drove around for 15 minutes nothing.

i'm leaving the parking lot, feeling like "hm. maybe it's gone" since they checked the torque on some bolts. and shit you not, the first time i push the clutch in to turn out of the lot. -clunk-