BMW E90 335xi Making noise sometimes (Knocking/Rattling)

[Mayank]

BMW E90 335xi 2011 is making loud noise sometimes. It makes noise
1. When accelerating over 70 miles and sometimes in lower speed when I remove foot from gas.
2. When I keep the car in park and press gas, sound comes when RPM is over 2000.

Showed it to a local mechanic, when changed the oil yesterday. He said, they haven’t seen this kind of issue before. According to him, sound is coming where engine and transmission are connecting. His guess is either Torque converter or Transmission issue.

There is no performance difference i see, it’s just the noise coming on and off while driving at high speed. Sound is coming under the hood, somewhere at bottom. Few months back i had whole gasket changed. Not sure what is causing, need help on how to diagnose this issue. I just don’t want them to Open the transmission and make it as a very costly fact finding mission. What should be the approach in this case?

Topic

[Mike]

Start with simple things first.

The first thing I would check would be loose heat sheilds and other loose components of the exhaust system, like hangers and such. Things like that can sometimes rattle/clank intermittently.

Another thing to check for for would be failing engine/transmission mounts. They can seem fine under most conditions, but make themselves known under a particular load range.

[Author]

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