I've had a look around on the forum for an answer to this but cant find anything that exactly matches.

Vogue TD6 2006 BMW

When starting from cold I regularly get a low-mid pitch 'howling/honking' noise that I think I've tracked down to the area of or near the battery compartment/pollen filter. It definitely at the top and rear of the engine bay and more on the nearside than offside.

I've tried the rubber hose 'stethoscope' approach to try and isolate the sourse without any real success and the noise always disappears after a couple of minutes of driving.

It driving me mad

Any helpful suggestions gratefully received.

have you checked for splits in turbo hoses

Yes all turbo hoses appear to be fine.. No whooshing noises. Sure noise is coming from up high in the rear of the engine bay/heater intake/battery area.

FBH would be my guess, if one is fitted. L322 3.6 TDV8 Vogue. 07MY
ML 320 7 Seat full leather etc. (The Black Pearl)

Unless I'm mistaken (quite possible BTW) the FBH is in the wheel arches?

Im not discounting this but why would it give the noise so high up in the engine bay area?

My little grey cells are jangling about a post (can't remember where) that i read about some sort of 'flap' in the fresh air induction unit but i cant find it again any where.

Again thanks for the replies. I love a good mystery

FBH itself is in the engine bay, next to the N/S suspension turret, but yes the exhaust for it is in the wheel arch. 2004 Vogue TD6 - Remapped
2008 Porsche Cayenne S
1998 Lotus Elise

I'll take a look at the FBH and see if I can get any further. Also I think I found the other post I was referring to. It was to do with the "HVAC recirculation valve". Anyones thoughts on that one? Is it easy to get to/check/replace? Many thanks.

Found the following online which sounds exactly like the problem. Will do some investigation with the FBH when the weather improves. Thanks again for the replies.

Click image to enlarge

Click image to enlarge