A weird horn noise when engine is rev'd

Probably the pipe on the crank case valve:

RealOEM.com BMW R53 Cooper S Crankcase-Ventilation/oil separator

The thicker rubber pipe on part 2 (just to the left of part 3), had become stretched and "farted" when you blipped the throttle.

I bought part 2 from the dealers (about £8), whipped the rubber hose off the end, and replaced mine, and secured it with a jubilee clip (part 3). All sorted!

You can do a quick check by leaving your bonnet opening, and blipping the throttle whilst you look round the bonnet - you should see the hose bellowing.

Thank you for that info I have had a look and it hasn't got a clip on the hose so I shall be putting a clip around it and see if it makes a difference .....
Thanks

Mine went on me the hose goes soft and calapses making the noise you decribed, i just replaced mine with a bit clear air line i had lying around does the job perfect .

I have this too, anyone tell me what other parts need to be removed to fit the new hose?

Or can the soft hose end piece be replaced without removeing any other engine parts? Please help... Thanks..

Like oli said, pipe on the crank case. Had mine replaced a while ago and the noise stopped.

Thanks yeh, I know its the pipe....What do i need to remove to get access? Cheers.

Btw the tech term for this is "Moo from soft pipe" :laugh: