That doesn't make sense at all. Can you record a video with direction to the supercharger belt, when this noise appears?
Have you tried to remove the charger belt and try to reinstate the noise? (You will get a battery warning, but this is not a problem).
Inside the M45 are only 2 gears and the rotors. It could be that the rear bearings have so much play that the rotors get in touch. To verify this you can remove No 17 and look at the rotors for marks. To remove it you need E12 sockets.

 

@112233 , thanks. Apologies if this is a dumb question but how do I loosen the tension to temporarily remove belt 2 (“II”)? Do I need to twist pulley 7 or 8 in the earlier diagram? & what tools should I use? (Also note I have an M111 engine) Thanks!

 

Oh Lord how did I miss this thread! If you turn your steering wheel all the way hard and either direction to the lock point it will make a noise no matter what! Don't keep it at that State because you can damage the pump! Typically this is nothing more than low steering fluid. You need special European fluid which is available in most parts stores the name of which escapes me right now . Made by petroson . If you look very closely at the fluid dipstick which by the way have you even found it? It's under the first engine cover . There are two markings on it one for when it's cold 25 C and one for when it's hot which I think is either 80 or 90 C printed on the dipstick . Check it when it's hot make sure it's not overfilled . And make sure you put the right stuff in at the right level or you will destroy your power steering pump . If it's over filled get a turkey baster and suck some out .I periodically suck the fluid out as much as I can get and replace it with clean fluid. Amazingly the PS pump has never gone bad on my car . PM me your phone number, I'll give you a call to help you out rather than this back and forth. I too have owned my 02 C230 for 23 years purchased in January of 2002 and put 262,000 miles on it still running but with a leaky head gasket that doesn't affect the operation of the engine amazingly but has coolant leaking out. And I also just purchased another one that only had 36,000 miles on it. In any case during most of that time I've done my own repairs and I can help you probably figure this out.
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​​​​​​As far as the way it reacts when you first start it cold that's normal for this engine. Many engines use electric air pumps when they start but this one uses the supercharger to heat up the Catalyst. It also keeps it in first gear longer before shifting to second also to try to warm up the catalyst to reduce emissions. The recirculation valve closes for about first 30 seconds and the car sounds horrible and Shakes because of it being forced to pump the air into the intake somehow that pushes it into the Catalyst or something I'm not entirely certain how that part works . And as the car gets older and your engine mounts begin to fail it will shake even worse and make more noise. How do I know this? Because on my 260k mile vehicle the engine mounts are shot. But at this point I'm just using it as a backup vehicle. This Behavior at startup is normal I doubt there's anything wrong with that or the car. Don't buy a new supercharger or recirculation valve! I think your mechanic is just firing the parts cannon at you since you keep complaining about a problem that is probably just normal for this vehicle. And by the way the power steering pump and the supercharger are on on two separate belts. After 2002 they switched to a different engine that only has one belt.
yes of course the sound goes away when they remove the belts! The supercharger isn't blowing any air at startup or any other time and therefore it's not doing its startup routine where it pumps air into the exhaust. God your mechanic is a freaking idiot he knows nothing about this engine.
​​​​​​ as far as tools, to work on these cars you need Torx sockets and torn sockets.
I wonder if you've even figured out how to get the air cleaner off yet?

 

The pump can run without oil for 50 km without damage, there was a TSB that you should fill to the maximum or a bit above.