Getting a low humming sound coming from under my bonnet. (Sound is just like someone blowing over a bottle)

Narrowed it down to the vacuum pipe, pump to servo. No obvious leaks. I've pulled the pipe from vacuum pump and the noise stops, place it back on, and noise starts up again.

Anyone had this before? I'll replace the pipe (as I can see no obvious leaks) to begin with, hopefully not a servo problem. The brakes work fine.

The garage thought it was my turbo failing! Won't be going back there again!!

Richcl wrote:

The garage thought it was my turbo failing! Won't be going back there again!!

Oh gawd. That's why I still do my maintenance on my own. Even though it's a PITA at times.

Funny, tho, I've had this noise as well - though very rarely. If it is the same noise. Mine is rather loud, but goes away again too quickly for me to locate what it was. I thought it had to do with the heater/vents/air control flaps. It sounded like it was from the underhood(bonnet) area but for me it has only happened at speed (97% sure its not trim/windshield related). And the 'blowing over a bottle' describes it perfectly.

Searching a BMW forum would be my next step - but I'm too tired tonight...  
RRC 2Dr, RRC 4Dr,
P38, and 2 L322s
(wife thinks I'm nuts - prob right, too)

The other way to check it, is with engine running, depress the brake pedal several times to the empty brake servo, then stop pumping brake pedal when the noise dissapears then as air preassure returns, so will the noise.

I'll be changing my servo hose to hopefully fix, and also shorten the route of hose, it winds around the engine to get to the servo, can only think that it's because of adapting to RHD from LHD applications.

Well today the car has been to dealer and plugged into diagnostics, nothing found...

So got underneath and used hose pipe as stethoscope, placed it against turbo actuator and it seems the noise comes from this, placed against turbo itself, and it was quiet.

So now trying to locate an actuator.