[Masuke]

Hello,

After switching to an aftermarket downpipe, I began to notice this noise as well as feel increased vibrations inside the cabin. The noise occurs during cold start and when I drive, most noticeable around 1,300-2,000 RPMs in Comfort (it produces less vibrations inside the cabin in Sport, but the noise still persists).

I have been chasing this sound for a while. I tried different downpipes (current one on the car is VRSF catless), and replacing the turbo v-band + gasket. There was an exhaust leak where the downpipe slides into the mid-pipe, and upon several attempts to reposition it (throughout each downpipe I tried), the leak still persisted as well so the downpipe was welded to the mid-pipe.

I'm not sure what else this could possibly be and would appreciate any feedback. Could this be leaking from somewhere upstream? Perhaps the v-band is leaking? I've heard of wastegate rattle, is this what it is?

I tried to capture the sound and have posted it on YouTube, the link is down below.

Thanks.

2014 BMW 535i xDrive (N55 PWG)
< https://www.youtube.com/shorts/Ik8JzcUClp0 >

[95blkmax]

The cold start sequence on our engines is pretty loud. Especially with a catless downpipe installed. It's not the best quality audio but I do hear a metallic raspy sound.

Does it go away once the RPMs drop from initial start? Do you have any tuning software? If you had something like MHD you can de-select the cold-start sequence and it would just start and rev up to like 900 and drop (but if the engine is cold and it's cold outside it may bug and surge until it stabilizes). I wouldn't recommend this as a fix but as a test to rule out it just being the normal cold start sequence that you're not used to experience without the stock catalytic

[oczko98]

Got the same sound in my n20 with catless dp. Its just a coldstart sequence I think.
And it sound obxnous :/

[SWFLf10]

I know after installing my high flow downpipe I had an annoying rattle during the cold start sequence. I believe it’s my wastegate as I’ve got quite a bit of miles on the car (170,000 miles as of now). I can manually move the wastegate linkage by hand and replicate the rattling sound, so I’m pretty confident that’s what the issue is.

I’ve since coded out the cold start sequence through bootmod3 and it now starts quieter and doesn’t have the rattling present.