I've listened to what I assume would be the same rattle, clatter (sounds vaguely like a diesel) since I bought my truck. The noise in mine comes from the blower. I loosened the tensioner and slipped the blower belt off the idlers and started it up, even drove it a few blocks. No clatter. Put the belt back on and the noise is back.

Now that I know what generates the noise, I kinda like it

From all the threads I've read there might be more than one source for a similar sound. Obviously changing the oil would not affect a blower noise. So I don't know, but I do know where mine comes from and it was worth a few minutes to try it.

My guess is that the blower is somewhat like the old motor driven sirens on emergency vehicles. Most of you wouldn't remember (except maybe Chikenears) how the sirens would wind up and then down until when they nearly stopped there would no longer be a high pitched scream but a low flutter, nearly like a small engine.

Well I guess that proves I'm getting old, but when I nail it and hear that blower whine I lose a few years and that feels good!

 

Dennis: If it's a bad belt or when you decide you need to change it, get a Goodyear Gatorback poly belt--guaranteed no s/c belt slippage . Of course, it the noise is coming from one or more of the pulleys..............

Dan

 

I've got a "PolyCog" belt. I don't think it's belt slippage or a pulley bearing!