W210 E300 belt question
 

A few months ago I replaced my belt tensioner and belt because the tensioner was rattling. Now, the same rattle is back and the belt is now squeaking as if there is insufficient tension. By tensioner I am refering to the blach shoch-like looking component.

Bad tensioner?

Should I have replaced something else while I was in there?

Did you replace the black shock or the metal spring in the rubber
sleeve?
Dr.D

The shock absorber only dampens the belt deflection. The Spring keeps the correct tension on the belt.
Sounds like you need another shock & a new spring.

Thanks, guys. I replaced the black shock because that is what was rattling. I assumed that it got tired.

Could the shock start rattling because the spring is bad?

Yup, the spring will kill the shock. Too much belt tensioner
movement for the dampner to handle.
Replace them both.
DR.D

Well, I replaced the spring and shock yesterday. The belt is still making a whistling/squeaking noise!! The belt itself looks practically new - about 60K on her.

What do you guys think?