u/InspectionDue6586

Hi All,

My E90 335i makes this loud metallic rattling noise from around the exhaust/drive train area. In the clip above I had to park on an incline to a basement carpark to reproduce the sound. I would describe the sound as "hollow" and metallic, such as the exhaust pipes. It sounds like it is coming from around the exhaust/transmission/driveshaft area and is ever so slightly audible through the center console from inside.

More info about the sound:

• It only happens sometimes. I cannot figure out exactly what the conditions are for it to happen. Some days it is rattling the whole drive, other days it doesn't rattle at all! The *only* potential variable I've noticed is that as I drive it, it can sometimes start rattling or get louder.
• Rattle is most noticeable under light acceleration and in low gear such as taking off from traffic lights, driving up car park ramps in multi-level car parks, or in drive throughs where the sound reflects off the walls. No rattling when under hard acceleration or at high speed.
• No noise on reverse, coast, braking, or turning. No warnings lights on dash or error codes in MHD/Bimmercode. No vibrations or weird behavior when driving the car. There are virtually no mechanical issues that I can find related to this noise!
• It can be made to happen by parking on an incline, but does not happen when on level ground. It also doesn't happen when I rev the car in neutral.
• I've had a look underneath myself and checked for loose bolts, brackets, and heatshields. Its also been looked at by several different mechanics and all of them failed to fix the issue. Some have tried adjusting the exhaust/downpipe to no avail.
• My car has the VRSF high flow catted downpipes. Transmission was serviced about two years ago.

Any help would be much appreciated!