So i have an interesting problem. When i rev my car, i get this strange noise coming from the air filter box, almost as if there is a mini maize mill in there. The noise is even worse when i am driving and very noticeable at around 2-3000rpm. I am pretty sure people think i am driving a diesel car now. also feels like the engine is loosing torque, as in revs go up but "mr drive me" takes some time to pickup speed and shift gears up. So last night my brother and i removed the flexible pipe leading to the air filter intake and rev'ed the car between 2-4000rpms. That air filter box is racket really coming from the air intake system, and when i release the throttle, the thing seems to be blowing air out of the filter intake side.

a bit of history on this car. I hit a speed bump at around 100kmph sometime back, i managed to crack my TB pipe and the black hose leading EGR valve came loose. i drove the car some 200Ks with this problem before i could replace the TB pipe and hose. After this fix that's when the funny noise issue showed up.

does anyone know what the problem could be?

Well, look at the job done recently.

You are right, or at least i think we are heading in the right direction. I took apart the EGR valve apart from the minor carbon buildup everything seemed ok, up until i did a cold start. I noted the valve seemed to be stuck in one position, so i think i must have a vacuum leak. Will try to replace the vacuum hoses and see what happens next.Thanks

I have the same issue with my car now. And cannot figure out what causes it. And when car is hot it goes away.
What was your fix?

I know the post is old but would be really great to get some feedback to help me on my way

Could it be related to the secondary air pump/system?

Does a w204 diesel from 2011 even have secondary air pump?

I did not find anything about it online

Unfortunately I do not have any experience with diesel engines. The engine above is the m271 so im thinking the issue probably is not the same.