noise
 

I had a terrible noise coming from the front of the engine in my 97 C230. Narrowed it down to the belt tensioner and pulley assembly. Replaced the tensioner, pulley and shock. the noise was gone and everything was great for 500 miles. Now at idle the tensioner is vibrating and the noise is back. If I increase the rpms the belt smooths out and no noise. Any ideas?

I am assuming all tensioner components you replaced were new?

Sounds like the bushing attached to the tensiouner shock has worn out. Typically announces itself with a clanking sound at idle but smooths out when driving.

About $2 fix if this is the case. One test to perform is to take a screwdriver and apply pressure to the shock mount while the engine is at idle and see if the noise goes away. If it does, there is your problem...