I've just spent some time in a bad traffic and have noticed a strange noise coming out from under the hood.
I can hear it only on 1st and 2nd gear. It works in about the same moment when blow off valve in petrol engines. But instead of pssssss it is more like kkhhhh. So when I release accelerator (and I think I press the clutch) it goes khhhh. Plus it can be heard only when revs are going down from 2k rpm. I can't hear it when it goes down from lets say 2500rpm.
I've got a visit booked in a garage on friday for service and overall check but need to drive to work for next few days and am not sure if it's safe.
I can hear it on 3rd gear as well. So I can assume that it is the same on all gears but it is hard to hear it at higher speed because of road noise etc.
It does happen without releasing clutch as well. It just is more noisy when revs go down quicker so when I press clutch.
It really sounds like some kind of valve or something.