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      04-06-2020, 02:40 AM   #11
NathObeaN
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Drives: M2 Competition (MY2021)
Join Date: Jan 2018
Location: UK

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So just to post an update here, I recently gave my car a full service including changing the air filter. The sounds is noticeably reduced... my suspicion is that either the old air filter was past its best or it wasn't secure properly perhaps leaving a small gap for air to leak.

The other things I changed, but I can't think of any reason it would cause the noise to change:

Brake pads
Brake fluid (flush)
Engine oil (flush)
Oil filter
Ignore. I thought the issue had subsided but after some hard driving, it came back.
Had the same issue since 5000km to 30000km with the sound increasing over time, then on highway high speed drive the car went to limp mode. Cleared the codes using BimmerLink and ordered: charge pipe, turbosmart diverter (plumb back) and wagner IC. The sound is completely gone. Car is whoosh wistle dead quiet. Suspect a leak somewhere in the system.
Hi guys, just to report back I finally found out what the 'issue' was. Turned out to be my MPE.

This is going to sound stupid but i was driving the other day with the exhaust valves in their normal/closed state and floored it... there was the sound. Immediately a theory jumped into my head which turned out to be true - maybe the suction noise is coming from the exhaust, not the engine bay. Maybe, the sound is from the pressure build up behind the closed valve which is seeping through the tiny gaps around the edge of the valve. Yup. It was exactly that. Open the valves and the noise completely disappears. Close the valve, the suction/whistling noise comes back as the exhaust gases try to escape through the tiny gaps around the valve.

After almost a year of scratching my head and inspecting the engine bay I now feel incredibly foolish!
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