Noise and diagnosis

[PSQ777]

For the last few months I have this intermittent chirping noise coming from somewhere behind me in my M40i. Some days it never happens, others it is frequent. I was banffled as to what it could be. First I thought it was the suspension, but bouncing the car and driving over different surfaces didn't show any consistent behaviour. Next the brakes were potentially the cause, especially given that it seems to happen when coming to a stop. But I couldn't get that to be consistent either. One odd thing was that it always happens as I slow down to turn in to my drive.

Finally this morning I think I found the cause. I had just started the car to take one of my sons to school, and he announced he had forgotten something, so ran back in to the house. I got out of the car and stood there fiddling with my phone, and suddenly the car chirped ! So not brakes, not suspension. My thoughts turned immediately to what is active on the car. Exhaust valve seemed likely. So I did the school run in Sport+. No chirping at all ! I did a bit more research and found comments on various forums (M140i/M240i) that it's a known issue. My car will be going in for a service early next year so I'll get them to take a look at it then. I can live with it for now, or just drive everywhere in Sport+

Anyway just posting this in case anyone else has a similar issue.

[deltasierra]

Are you sure it isn’t coming from the speakers behind you.

[PSQ777]

Are you sure it isn’t coming from the speakers behind you.

Absolutely. It's much louder when I heard it standing outside the car, and it's loudest in the car when I'm near a wall. From what I've read an M40i on startup has the flap open, but it closes again after 30-45 seconds which fits with what I heard this week.

[crz4]

It's the flap opening and closing. You will hear it much better/louder when you are driving in a parking garage and the sound reflects from the walls.

[PSQ777]

It's the flap opening and closing. You will hear it much better/louder when you are driving in a parking garage and the sound reflects from the walls.

That's what I'm thinking. To make it clear, it is really loud. Not just a little chirp. M40i cold start, and it is very audible over that.

[PSQ777]

Just in case anyone else has the same problem mine is now resolved. It was the active flap in the exhaust. I bought some lithium grease today and used it on the flap. Took the car out tonight and not a single squeak ! For months I've been annoyed by that noise and I fixed it in less than a minute.