A question for the forum: I'm hearing this odd noise when I accelerate slowly. It's a groaning hydraulic kind of noise that lasts a second or two - but is always followed by the sound of the BPV valve. Usually happens when I shift from 1st into second, or second to third, and gently accelerate. I've seen many threads that say that people can hardly hear the turbo's in N54/N55 engine during normal driving..but I hear all kinds of hisses, whistles, etc (especially when it's cold out. As it gets warmer, the turbo sounds get quieter). Sometimes when I hear the odd groaning noise, it almost feels like something is slightly stuck because I occasionally get a slight hitch in power, and when the noise stops, everything seems normal.
I've brought it to the dealer several times now to investigate this, as well as an independent mechanic, and they all say they can find nothing wrong. There's no warning lights, or codes. But to me, this sound just doesn't seem to be "normal". Could it be a faulty BPV valve?
Because the noise sounded sort of hydraulic, I've had the brake/clutch lines bled, and fluids replaced, etc. But that didn't solve it. I did get a new gearbox and slave cylinder recently, so it might be related to that.
How does a BPV operate? Is it mechanical, or driven by pressure only? Is there any part of the turbo that could make a noise like this?
I suppose since the dealer and a local shop told me there's "nothing wrong", I should just try to ignore it - but part of me thinks this could be an indication of something that could become a bigger problem later...
Any thoughts or suggestions would be appreciated.