An idle video is here:

https://youtu.be/Hu_bPUY9_VA

I used a stethescope but had a hard time pinpointing it.

Could be the tensioner pulley, idler pulley, but I guess it could also be the vacuum
Pump or ps pump. It’s coming from that side of the engine…

I can’t say I’ve heard a failing vac pump, especially on a 603.

Any thoughts on the noise? I may just get all the parts, but I’d really like to be better at diagnosis.

Thanks!

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Take the belt off. Will eliminate the vacuum pump or not. As the source. Also you can feel the pulleys for bad bearings if it is not the pump. If a 603 you want the protected bearings in the vacuum pump version. If new vacuum pump is needed and too expensive a used updated type pump might be located.

One type the bearings can get out and to a lot of damage. The other updated version the bearings are sealed in. You may already have the right version but that has to be checked. i though I saw somewhere that bad bearings in the newer version pump can be replaced.

If by chance it is the vacuum pump. Do not drive the car until it is dealt with.

The vacuum pump bearings do not turn full circle. They more oscillate back and forth I think. So they would not make the same noise as a bearing in more normal service. If bad you stll might get a noise though. I might be wrong. I see by your list of cars you probably do not have the problematic version of a vacuum pump. Your 603s are too new. Even as old as they are.

Good point about the belt. I might pull it tomorrow AM when the engine is cold and see how it all sounds...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

OK so I did the belt removal and ran the engine. It’s definitely not from the vacuum pump. This was a cold start with at least one bad GP.

https://youtu.be/8_0kdJ0oySI

I then checked the pulleys. Thoughts on the idler? It spins nice but is somewhat noisy.

https://youtu.be/GefNV_ESpd8

I do think the tensioner itself may have some issue, note that when I push the tensioner body down, it quiets, like shown here:

https://youtu.be/aOEkssBxeqs

Can’t really tell if the tensioner bushing is bad. The engine is clean, this tensioner was used, I was told that it was a used part fwiw.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

My '97 606 has the same tensioner and makes the same noise. I understand that there is a special ratcheting alternator pulley that should quiet the noise, but I have not tried it yet. On my car the top of the shock was tapping on the head, so I used a rubber washer between the shock and the engine head, which helped reduce the noise to bearly tolerable. If you solve the problem let us know how you pulled it off.

__________________
'97 E 300 D

Pulley is not normal with no load. Could be far worse with a load. The dynamics when the pulley is operational on these serpentine belt systems.. The intended alignment can be off a bit providing an unintended type loading in a bearing as well. I would change the pulley on general principal or change the bearing in it if possible.