Hi everyone and sorry for not introducing myself yet but I have an urgent question to ask. Our 2.0 Z4 has suddenly developed a noise in the intake manifold! when revving the engine and shutting of the throttle quickly a noise which sounds like a clatter or a clacking sound. This is not valve train noise or timing chain noise as it is backside of the engine ( bulkhead end ) I have had all pipes off today and inspected the throttle valve itself and all is in good order with no apparent play. The engine sounds very smooth until the revs are dropped, it's the same when driving and changing gear or free revving without being driven. Any idea's? Thanks for any help ok

Hi Andy...welcome to the club!

Not entirely sure which component could be causing the noise but I wonder if any other members have experience this before.

Has it just started or has it been since something has been disturbed, say during work on the engine for example?

One other cause may be the Vanos system (if fitted)...and if so, maybe just a case of replacing the engine oil to quieten down...just a thought!

Cheers   Trevor - Admin

Thanks for your reply Trevor, my partner has just come home and is saying that the car has lost power and is not very sharp on the take off so to speak. I forgot to mention the engine management light is also on. Everything looks fine under the hood although the car does sound a little bit more throaty from the engine bay but I not detect any blowing from the exhaust at the front end. Thanks again for any clues before I decide to take it to a dealership for checking.

It is not fitted with the Vanos system, just double checked. Does this engine have swirl flaps and if so this could be the noise I am hearing, from the 4 black intake tubes/pipes the noise seems coming from the 4th intake tube ( bulkhead end  )

Just checked lol, no swirl flaps on a petrol.......Doh

Best bet is to take it in for a scan to see what the codes are for and go from there really.

Hopefully, nothing too expensive 

Checked all exhaust joints and non blowing, I have removed the inlet manifold because the noise is definitely coming from the unit. I can see the chambers inside actually move up and down inside by a black solenoid type unit on the front near the throttle body, does anybody know how this works? BMW want the car in so they can charge me the earth lol but I have worked on all of my cars over the yrs so this will be a last resort but info on how the manifold works would help. Any idea's??? 

Here is some info on the variable acoustic manifold system (if it's the same system as yours) 

http://www.forzagb.com/tech/

http://www.ebay.co.uk/itm/4-x-22-mm-Swirl-Flap-Flaps-Replacement-Removal-Blanks-Gaskets-for-BMW-2-0-M47-/181544146050?hash=item2a44dfd482:g:9DgAAOSw5IJWflKT