I noticed my tensioner pulley moves back and forth some while the engine is running..is this normal? It doesn't move far, just 1/2" or so. Or are you talking about the tensioner pulley bearings? If the bearing is bad I guess it would make a noise.

 

We have a 95 Blazer with a 4.3. When the truck is riding down the road or sitting steal, it makes this god awful noise, that seems to be coming from the front top of the motor. We have tried what you've suggested in the above statement. (Pushing on things til it stopped) We've looked under the hood and under the motor and still can't seem to find what is making this loud, awful, sound. What might you think it would be or where it might be coming from? Some people are saying that it's in the motor but when you take the valve covers off, there is this tapping noise that we can't seem to figure out where it is coming from. Can you help with this or at least kind of point us in the right direction? We sure would appreciate it. Thank you.

 

It sounds like You are experiencing the same problem I am. Your tensioner has weakened and needs replacing. Just to clarify when you turn on the A/C you can hear the rattle easily, When you look at it is the tensioner being pulled all the way to the point where it is bouncing off of it's own mount. If you answered yes to these replace your tensioner the spring has weakened.

 

I guess I should have replaced the tensioner and pulley when I changed the belt and water pump some time ago.