Muffled rumbling noise from the engine compartment of a VW Golf 5 TDI BKD

Hello everyone.
I'm having a problem with my Golf 5 TDI 2.0 16V BKD, manufactured in 2004, with a DPF, and I'm simply unable to find the cause. It has 245,000 kilometers on the clock.
'Everything is fine up to the fourth gear. When I shift into fifth or sixth gear, there's a dull, rumbling noise coming from the engine compartment, as if the air filter has been removed. I've searched everything and can't find anything unusual. When I shift back to fourth gear, the noise disappears abruptly. The engine speed or the vehicle's speed doesn't seem to matter. There are no error codes stored in the engine control unit. Has anyone else experienced this, or have any ideas what it could be? Shortly before this, the clutch (Valeo), pressure plate (Bosch replacement), throttle body, and EGR valve, MAF sensor, were replaced or renewed. The car recently passed the technical inspection (TÜV) without any issues. The car drives well, except for the aforementioned noises. I suspect that the long or short EGR pipe might be leaking.' Or Turbo? Intake manifold turbocharger? It can only be determined after disassembly. But shouldn't error messages appear there?
I am very grateful for helpful answers.

Hello...

Your BKD engine probably doesn't have a DPF, just like mine! Euro 4 WITHOUT DPF!

Sometimes, my car also makes a buzzing sound, for example, when accelerating from low speeds.
Revolutions. In my case, it's almost certainly some aluminum heat shields in the area of the turbocharger, extending towards the driveshaft. It is also directly screwed onto the exhaust manifold.

There used to be a problem with the flexible pipe connecting the turbocharger to the exhaust cooler - it would whistle and then smell like exhaust fumes.

Theoretically, you could replace the engine mounts and the torque strut (is that what that part is called? I mean the connecting brace between the engine and the transmission) when you're doing the mileage check, as they're probably not brand new anymore. (I haven't replaced them - currently at 360,000 km!).

"Turbo... hmm... definitely not something you can ignore with a BKD engine. Mine was due for replacement at 200,000 km, but you'd almost certainly get an error message before that happens..."

SG
Manfred.

Hi alevus,

If the problem only occurs in 5th and 6th gear, it theoretically cannot be caused by the engine or its components. I would tend to think it's related to the transmission.
Since the clutch was recently replaced, I would go back to the workshop that did the work and have them take another look. Although, the clutch itself doesn't directly have anything to do with the 5th and 6th gears. Someone might have made a mistake during the installation or removal of the gearbox.

Greetings,
Hannes.