Guys this has been driving me crazy hunting down this hiss under moderate load. I haven’t been able to replicate it in my driveway only while driving. Found an intake leak, exhaust leak and serviced my supercharger none of them are the culprit, starting to think it’s just part of the intake noise. Of note I think everything is stock JCW but my JCW filter box seems like it has the flap delete also. Hopefully someone can tell me if I’m chasing a ghost or offer some new test!

 

I couldn't hear anything from the video....
Any fault codes?
Any discernable loss of power or otherwise?

 

+1 any codes?

take the box out and see of the noise goes away? just something to try.

 

No fault codes, no loss of power or anything like that, purely a hiss/metallic hiss at that load range.
Hoping you guys can hear it in the video but I don't know how distinct it is over phone audio.
Might try taking the box out, or just the filter and see if it changes volume or pitch, good idea.

 

I can't hear it either. Maybe have someone ride along to see if they can get an idea of its source.

 

Alright, filter box out, new clip, I can hear the noise pitch better on my phone than my computer speakers for what it’s worth. It’s like a buzzing bee. Would the BPV sound like this if it was acting up?
Appreciate the help on this one, driving me crazy.

 

Sorry I can't open the files, but since you mentioned "metallic" and "buzzing," could it be a heat shield rubbing on something it shouldn't?

 

I can just barely pick up something on top of the exhaust note, but I don’t know if it’s the sound you’re referring to. It sounds more like an almost metallic rattle to me than a hiss. Do you have anything loose in your cabin or glovebox? Impossible to localize that sound from a phone clip.

 

We were BMW fanatics for many years. Back in the early days, 2002's were called "whispering bombs" because of a weird whistle that emanated from them at speed. Turns out it was the stainless steel trim that was attached to the rim of the hood. It vibrated and created a whistling sound. I'd suggest that you look for something that could vibrate at speed.

 

^^^Interesting^^^....
Although I couldn't hear anything that struck me as unusual from the clips, Perhaps check the intercooler cover to insure it is secured?... Or maybe the heatsheld above the header?....

Speculating on the notion that something maybe loose -
I remembered reading a post here, a while back; where an R53 owner's hood scoop suddenly blew off while driving down the interstate.

 

many things can hiss or buzz. does it correlate to enging speed or wind speed?

 

Okay, gathered some more data with an OBDII logger, it had a handy MAP readout, hopefully accurate.
At idle it's around 9.5-10.9inHG, decent vacuum? Google said this is low indicating a possible leak, but I would have guessed a higher number was worse as far as leaks... Maybe that's a gauge pressure vs absolute pressure issue...
I hear the sound around 20-30inHg so in that crossover region between vacuum and boost it would seem... Denver today is around 30.2inHg... it seems like some mid throttle issue, if I get on it with more throttle, I get a good pull with all supercharger whine and no sound...
Anything else that might be helpful to diagnose?

 

Maybe the bypass valve leaking at lower revs then opens around 2800 rpm?

 

the bypass valve actuates right at the crossover from negative to positive air pressure (iirc). so you could be on to something

 

BPV seems fine, small amount of light around the edges, I think that’s normal based on what I’ve read. Not loose or floppy, I can actuate it with suction on the tube, I was a bit surprised on how progressive it is rather than a quicker open/close. I would guess that is why the 20-30inHg range would make noise if this is the culprit, the gap would be somewhat tight but not closed.

Odd thought, why does it actuate from pressure on the plastic pipe side? It seems like that section would always be at vacuum and never quite get to atmospheric based on its position vs the throttle body and supercharger… seems like it would never really be closed.

Maybe I just need to adjust my driving habits, but it is annoying…

 

i hear those are very inexpensive. might throw that part at it

you might have said this already. The airbox being off made no diffference?

any codes?

maybe a good smoke test would tell