flapping noice from unidentified engine part?!

[highstream]

Can someone please help me identify this item?
It´s "cover" makes a loud flapping noice when engiine is idle... is that normal? at least I havent noticed before :?
I can make it stop by locking the cover but then maybe its not working as supposed??
Here are the pics:

 

[ZetaTre]

I think it's the water drain from the heater housing (here)... I don't see how it could flap: is air coming out of it? The purpose of the flap it's to avid small animal (ie rats) to go inside and make a nest... You could remove the flap and replacing it with a net, like those use for door screen...

 

[srhutch]

looks like a drain flap, you need to ensure it will allow water to pass through

 

[highstream]

yes looks like that one... strange that air is passing through there... should I be woried? :?

 

[ZetaTre]

I know on mine no air blows out of it.
You could start by removing the cabin filter element and see if maybe there's something clogged.
Does it do it even with the fan off? What about with the recirculation?

 

[highstream]

nah dosent do it with the fan off so it must be related...
what about recirculation??
thanks for the help BTW

 

[ZetaTre]

I was asking if there's any difference with the recirculation on or off.
If it doesn't do it with the fan off then it's likely clogged: remove the cabin filter and check.

 

[highstream]

ok thanks!!
do you mean this one http://www.realoem.com/bmw/partgrp.do?model=BT33&mospid=47798&hg=64&fg=05

 

[ZetaTre]

No, I actually ment this.
At page 8 here you can find the instructions: I would suggest you go with Bosch. My guess it's quality is the same as BMW (maybe the BMW branded is even manufactured by Bosch) but price is much less. I bet you can order it at any auto parts store.
I never had the problem you are mentioning: my suggestion comes from the assumption that if the cabin filter is clogged when the fan pushes the air it can't go through and escapes from the water drain. On te Z4 I never took the heater assembly apart and it's hard from RealOEM to understand how the system works. I would start from the cabin filter also cuz it's the easiest and it's supposed to be replaced every oil change (15K miles)... That way you can also take a look and see if there's anything else in there clogging up the passages.
DId you notice any reduction in the airflow in the cabin? If so one more reason to think is the cabin filter.
Let us know...

 

[highstream]

Will take a look

 

[highstream]

Problem solved...Cut of 2millimeter strip of the lock and then it got enough clearance to flap as much as it wanted
Also noticed that it only flapped when stressing the aircondition system