A new rattle under the hood - E300

[slowmoe]

Pulling into the driveway today after a nice 300 mile drive on which this car performed wonderfully, I noticed a new rattle - diferent from the ones I have come to love and adore ofer the past several years - eminating from the engine bay. It happens at about 600 - 700 RPM while either increasing or decreasing the rotations. While excelerating up the drive with the window down it lasted long enought for me to think - "what was that?" then it was gone. I am able to keep my foot on the accelerator and hear the rattle consistently until I change the RPM's up or down.

What do you think?

[TimFreeh]

If this noise is happening on the 2.5 turbo check the serpentine belt tensioner shock. My car makes exactly the same noise. You can verify this by varying the speed of the engine with the hood up - you can plainly see the tensioner shock vibrating - at least I can on my car.......

Tim

[slowmoe]

I checked the tensioner and visually inspected while the wife was in the car holding the throttle at 600rpms - what a woman!!

Everything is tight!! Nothing is wobbling around. I am starting to get concerned about something internal - timing chain, rails etc...
Would a water pump make this noise?

Help is appreciated. Thanks

[slowmoe]

Well, Mechanic said that it was the fan tensioner. Does anyone have a step by step for this? I would like to try it myself and post the project.