Hi! Have this issue with my engine after my multi-belt snapped.
Does anyone know this sound?
Also a longer video here on my youtube.
https://youtu.be/YccjsCcLK9o?si=03DR9iXizAo9R86L

 

Sounds like the engine cover is rattling; that happens once the insulation blanket falls apart...it's just loose and vibrates. Pull the cover off motor and recheck.

FWIW: I removed the engine cover from my TDI once the engine blanket/sound insulation attached to it shredded, as it was moving around/vibrating, etc. I was more concerned about the cover wearing a hole in the myriad pipes/wires, etc., and so it now sits on a shelf rather than on the engine. But yeah, it rattled once the insulation blanket was gone.

I did look up part# to see if could find one, but the used ones are pretty much all same condition as mine...no insulation left on them, and the new one, if you can find one, well, the price for a new, plastic, engine beauty cover let me know I wasn't going to replace it.

 

Wish that was the case. It’s the same sound without the cover. I’m actually going without it right now as I left it at the workshop and unfortunately the knocking/tapping sound is still there.

 

OK, so listened to the longer video version and please tell us what's going on with that blowoff valve...jeesh that was a really loud pressure release at startup, so if you didn't modify that intentionally, then there's a problem. If you have done any mods to engine, now's the time to tell all.

You said the serpentine/accessory drive belt snapped?

Did you also replace the drive belt tensioner and idler pulleys (2 smooth and 1 grooved idler) when replacing the drive belt? That would be the 'normal' course of repair for a belt failure issue, as those are all parts of the same system. You could easily remove the belt from tension and check the idler pulleys for any play/bearing problems, as well as the water pump drive pulley for play and looseness (and check the weep hole at bottom of the water pump to see if coolant is present there, which means it is leaking/failing etc.

Since the noise just began after the serpentine belt snapped, that suggests it is related to the drive belt system still has a problem, which may have contributed to the belt snapping. There are other things that will create a noisy/rough feeling idle as well, like failed motor mounts allowing metal-to-metal contact to occur, etc., but that's also easy to identify; you just see if the engine is moving around as the revs rise; it shouldn't be jerking/twerking, or twisting about unless the mounts are bad.

I couldn't tell much with that cover obscuring/masking the source of sound combined with you didn't move the camera around the engine to capture sound level from different points, etc. If the sound goes away right above idle, then if may just be the water pump going out. Should be a lot easier to localize with the engine cover off. You can also just get a long screwdriver / mechanic's stethoscope to listen around different places (don't touch to moving parts) to help you identify exactly where that noise is coming from...you literally touch the screwdriver tip to a stationary point on car while it's running and other end to your ear, and move around to different spots to compare, etc.

If you make a video with the cover off engine, be sure to move the camera around both sides, in front, as well as over the top of engine to help see where the sound is the loudest.

 

Yeah the blow off sound I think is connected to the air suspension… think maybe I have some sort of leak and the air mounts up in there. I noticed that that’s where it releases air from the suspension when it lowers (release air) the air suspension. At the moment it’s a second priority. So to answer your question I don’t have any modifications.
The mechanic just changed the belt and the largest wheel that spins there, since it was wobbly. I will have to check the other things you wrote. I’ll try to also make a new video with the cover off.

 

first of all you should remove the acc belt and then start the engine:
-is the noise gone? Then the culprit will be some pulley, water pump, ac compressor, or power steering pump
-is the noise still there? Then the culprit will be something else

These engines have the vacuum pump built into the oil pump. so the oil/vacuum pump can make this noise as well.

 

+1
My working theory is that when your belt 'snapped', that part of the old belt got caught up and wrapped around some of the pulleys/shafts, etc.. and either the remnant of old belt is still there whacking against metal, or it has created a secondary problem.

I agree that if you release tension then remove the serpentine belt (take picture of the belt routing first), as this will allow you to isolate whether the noise is linked to the belt drive/ idler pulleys/tensioner system and what items they turn, or not. This is a quick, easy test, so long as you have the large star bit required to release tension on the belt (and take a picture of how the belt routes so it'll go back together, etc.).

NOTE: The serpentine belt runs the water pump/coolant, so you are not going to leave the car on other than simply to verify if the noise is still present w/belt removed.

I do find it odd that a mechanic changed your S-belt and the crankshaft pulley (those do break down on TDIs...torque and corrosion), and didn't notice anything odd. Hopefully they didn't reuse the aluminum stretch bolts that hold the crankshaft pulley on, as they will break.

 

So when the belt snapped the mechanic removed all the belt parts he could find and they were everywhere. Behind every wheel and so on. The knocking sound was also there without the belt.
When he changed the biggest wheel, crank shaft? No idea what it’s called he said it looked fine inside. But there was still an oil leak which looked like it was coming from the back of that wheel. So today he was going to replace the front crank shaft seal and when he did he pulled out this.
When that was out and he changed the seal
it all sounded a lot better.
Now there’s just a little tapping sound when I pull out the oil stick. I’ll try to upload that later.

 

Holy smokes! That belt really came apart! That's incredible.

 

Yeah, was thinking there was still shredded belt in there, so mark my bingo card for shredded S-belt square, lol; the problem is when they just snap from lack of servicing/maintenance, oil damage, or some other contributor, then they tend to get entangled within the drive belts system, and especially the drive pulley/crankshaft pulley as it is the one still spinning, so it just rips them apart...diesel torque...just gotta love it.

If you driving the car and it snaps, it generally makes a mess of the old belt and can possibly damage other wiring/hoses/vacuum lines/sensors routed within that region. I had a belt failure occur on diff car long time ago...happened right as I stopped at an overpass intersection after having just exited the freeway off-ramp the engine just died; talk about a sigh of relief that it didn't fail while on the freeway! New belt and it was good to go.

Bonus:
Also had a fairly positive 'belt failure' experience with my '96 Grand Voyager conversion van (lost it in the divorce, lol) because my ex drove it through some standing water and then the motor died. She didn't know what was wrong, and rather than have it towed to a mechanic, she towed it to her home, then had her friend or idiot cousin take a look at it, who gave it last rights and declared it as dead. A while after that occurred, then she offered it to me thinking it was dead-dead, and knowing I'd come tow it off so she'd be rid of it. After she told me what she did, I figured it was quite likely to be the drive belt had come off. (transverse mounted, aluminum 3.3L V-6 shoehorned into the front...an excellent engine!) She had gotten another vehicle, and so the van had just been sitting there non-running and taking up a lot of space, so she wanted it gone.

So the real kicker on that story is when I opened the hood up and looked it over to see if I needed to tow it or not, then I discovered that indeed, the drive belt was still there, in plain view, intact, and had just come off. WOW! I only needed to reset the drive belt, along with jumping the battery, and everything worked just fine. How ironic. It was a great vehicle, whether hauling people, furniture, garden/yard supplies like 30 bags of mulch, etc. Sometimes things do work out for the best.