[belcom]

I've been driving the car since november 2014. I am pretty sure I have not really heard this sound before but now for the last couple of months I hear a bit of hissing when I am in 1st or 2nd gear accelerating and then let go off the gas I hear this short hiss sound ever time. I can hear it much better in low gears because I guess there's less road noise at those speeds. It does sound like a blow off valve but because I can't recall the noise from before it makes me think perhaps there's leak... charge pipe maybe (fairly common failure)... I am not sure.

I can't really feel any significant loss of power or have any codes or lights show up. My 335xi is bone stock as far as engine goes and its N55 with 6MT.

So is your blow off valve audible at all? Should I have the dealer inspect for leaks or something?

[e92_enthusiast_1]

Yeah n5X dont have blow off valves. We have "diverter" valves. Instead of "blowing off" they get "diverted" back into the engine. The stock diverters are plastic and the valve spring is known to get stuck "open" and cause a hissing sound. That could be something to ask your dealer to check. Just guessing. It could also just be the air intake but you said your stock and usually you only hear more engine noise after installing DCI's. As Johnny said video would help a lot.

[Johnny Boost]

That sounds pretty normal to me. If you have an intake then it gets even louder. Have you had any limp modes or checked for codes? Can you take a video of the sound?