Hey everyone, recently I got a cheap 2006 330i e90 (about 130k miles), and it's now developing a weird rumble at mid-wide open throttle. When I first got the car, it was hardly noticeable and only at WOT in second gear or higher. It can be quite violent, making very loud "thud" noises, and shaking the whole car. It feels just like I hit a patch of continuous potholes.... It feels a lot like wheelhop, although I can't see why that would be it...
The rumble gets progressively worse in higher gears. When I first got the car, it was not violent, it felt more like a rumble. Also it would only happen if I stomped on the throttle. This is when I would feel it: (I was able to go past these RPM without feeling it, I just had to accelerate very slowly)
1st - never
2nd - 5000+ rpm
3rd - 4000+rpm
4th - 3500+ rpm
5th - 3000+ rpm
6th - 2750ish rpm
However now it feels way more violent, and is happening at lower RPM: (Also needs less throttle, half throttle will make it shake, where as before it was full throttle only)
1st - 6000+ rpm
2nd - 3500+ rpm
3rd - 3000+ rpm
4th and up - 2500+ rpm.
BTW the loud pounding / thud / rumble sound is seemingly coming from the back near the floor.. Maybe something with the diff/clutch?
At first I thought it was misfiring, but I'm not receiving any codes regarding that... Also I doubt it's the sparks as they were changed about 15k miles ago by a previous owner... could it be the coils? If so why is the sound coming from the rear? Also why would it be progressively worse in different gears then? Also it idles very well... maybe only under load it misfires?
Then I thought it could be wheel hop? However I doubt this because my car's not near powerful enough to break traction at half throttle, also why would it only happen in specific gears/rpm? (It's totally independent of speed btw. I can go 60mph no problem in 5th/6th, although if I try it in 3rd/4th it rumbles like crazy. Maybe due to the high rpm?
So maybe it's a clutch/diff issue? I could maybe see that being plausible due to the sound coming from the rear, also these 2 components need more torque in high gears to function... Perhaps the torque is making the clutch slip, and maybe the clutch is warped creating the noise / shaking? or maybe something's slipping in the diff due to the high torque of being at full throttle?
Let me know what you guys think the issue could be, or perhaps ways to diagnose it! I greatly appreciate the help!
