[nickkid09]

Car: E90 BMW. 2006 330xi 6 speed N52 engine.

Details. I have scoured all other old posts as well as other forums with no solution. Any insight or ideas would be appreciated. I am hearing a knocking sound coming from the front of the car, maybe the steering/suspension or engine compartment. I only hear the sound when the car is warm and I am driving at low speeds. As the car becomes warmer, the noise becomes more prevalent and even progressing from an occasional knock to a full on rattle. The noise mainly occurs when I am driving on an uneven road but start and stops will occasionally make the sound. I am having a tough time determining if it is a pop from a bushing or dense plastic banging against something. The noise happens both when the car is turning or driving straight ahead although the noise seems to be more noticeable when I am turning. The sound is not metallic. It is a knocking / quiet thud.

The below mentioned bad mechanic did not reattach the cabin filter and other plastic & electronic components that were removed when the struts were installed. I believe I have done my best to reattach all loose screws and clips, however some of the hardware mounts where broken during the job and I was forced to zip tie a few things to ensure they were secured. As shitty of a job this guy did, I do not believe the cabin filter and surrounding plastic is the culprit. The most frustrating thing is the car drives perfectly. It feels great, the suspension is firm and responsive.

Work done in the last year or so (after noise started):

Work Done by a not so trusted mechanic

1. New front struts and mounts
2. New sway bar end links

Work done by a trusted mechanic

1. Lower Control Arms
2. New Starter.
3. New alternator.
4. Rear Diff fluid
5. 4 wheel alignment

Work Done by me

1. Front and rear brake pads
2. Front Rotors
3. Rebuilt front calipers
4. Inner and outer tie rods
5. Sway Bar Bushings


Other things I’ve checked which have not solved my noise problem:

1. Removed plastic engine cover.
2. Removed under engine plastic cover.
3. Placed thick carpet tape between a number of different plastic pieces within the engine bay (cabin filter, air filter, intake, etc.) in an attempt to silence two parts knocking into one and other.
4. Checked and rechecked tightness of all nuts, bolts, and screws in the steering, front suspensions, and other components within the engine bay.
5. Checked brake calipers for play and loose bolts.
6. I jammed cardboard under the hood and the hood jamb to ensure there was no rattle.
7. Valve cover and bolts are OK.
8. Sway bar is in good shape.
9. Noise occur with or without brakes applied.

Things I have not yet attempted to try but are extremely time consuming and/or expensive:

1. Steering column & rack
2. Strut was over torqued during the installation damaging the strut or strut mount (can this be easily checked – everything looks secured and tightly in place.)
3. Sway bar end links possibly over torqued during installation.
4. Potentially other loose plastic.
5. Lower control arms (although they seem fine)
6. I’ve read some guys have had success replacing a “sheath” of some sort in the steering knuckle.
7. Look into possible loose drive shaft (I really think the sound is coming from the front).
8. Go through new suspension / steering components to ensure they are torqued to spec (god I don’t want to have to do this)

[Stupenal]

I would look into your strut mounts. When I was doing the suspension on my e82, I had a shop put the strut hats back onto the strut/springs, and they didn't tighten the top nut enough.

I installed the strut back into the car myself, and went for a test drive. I had pretty loud thumping sounds coming from the front that coincided with the smallest imperfection in the road. Since I had did everything myself with the exception of the top nut holding the strut mount on, I figured it had to be that. A couple blasts of the impact on the top nut while holding the strut rod with a vise grip (wrapped a small piece of old serp belt around the rod so the jaws didn't make any marks) and everything was good to go. I was able to do this with the struts mounted in the car - just needed to remove the OEM brace to get my impact in.

Another common part that results in knocking sounds is the sway bar end links. There's a hex portion behind the boot that needs to be held with an open ended wrench while you tighten the nut. This can be easily done by just removing the wheel.

Hope this helps.

[whyzee125]

Upper control arms? These usually wear at 3x the rate or so of the lowers.

[Efthreeoh]

Have you checked the CV joints on the front half-shafts. That's the first place I'd check if there is noise when turning.