Rattle around drive belt area

[TerribleTim]

Here's another cause for rattles besides the many listed on threads here besides alternator & waterpump.
My oem serpentine drive belt was getting old and cracked, so someone recommended Goodyear Gatorback. Ended up finally finding one online which I installed. After, I kept hearing annoying rattles when idling and backing out of the garage, etc. Turns out the Goodyear is too thin and flexible for this motor. I popped the hood and could actually see the belt vibrating between pulleys and making a rattling noise. I wondered what this vibration could do to the tensioner, so I broke down and replaced it with a regular thickness belt and the problem went away. Also, my mechanics say the grooves on the gatorback belts make it hard to see age cracking during inspections. Ironically, Goodyear markets this gatorback as a "quieter belt."

[sideshowalan]

Sounds like a problem with the tensioner itself, I've had zero noise from the gatorbacks on my old vibe and now my sienna.
The new belt you used probably just temporarily changed how much pressure is on the tensioner.

[TerribleTim]

Thanks. Good point. The Gatorback went on and off real easy compared with the new, much thicker belt, in terms of how much I had to compress the tensioner. The tensioner feels good so I don't know if I'd call it a problem as much as the Gatorback may have put it out of its design range, although the Gatorback felt tight enough and I ran it for over a year with no problem except the rattling.

I was worried that the belt rattling may wear out the tensioner was the main reason I swapped it out (not the noise). The Gatorback is thinner and much more flexible than the oem belt and its in the trunk now as an emergency spare. Btw the replacement was a dayco from Rock Auto which looks about like the oem belt. Because the rattle only happened at idle, I think the rattle was due to uneven or rough loads from the driven pulleys like ac at start up, or maybe a rough idle on the crank(i changed the plugs).
But you're right, the new belt is definitely squeezing the tensioner more. Don't know if this translates to more tension.