Hey all. 1998 Ram Laramie 5.9L 4WD.

I've got this weird hum/whine that comes from somewhere in the engine compartment. It's intermittent, and sounds kind of like a warbly whine. Imagine if you took an old-school hand saw and shook it and the blade started to "sing." Except it's a bit higher pitched. It will come in "waves" so to speak: start soft, and ramp up in pitch and intensity, and then wind back down. Maybe 15-20 seconds between "waves." If I shut the motor off in the middle of a "wave," the noise stops immediately. Other than that, it's unaffected by RPMs.

The noise only occurs when the weather is cold, maybe 40F or below. It seems unaffected by engine operating temp. It'll do this when I start it up, or after running for an hour.

The truck is a bit of a rust bucket. My theory is that maybe a piece of heat shield, or something else, has become weakened or broken and is vibrating to make that noise. I just can't seem to find what.

Your thoughts are appreciated!

 

Grab a section of hose, put one end to your ear, the other end kinda move it around in the engine bay, listen for the sound. The tube will act like a scope

 

Take off drive belt and start truck for a minute. If there is no noise, turn off truck and start spinning the pulleys by hand. Check especially, the AC clutch. If it feels chalky, bearing is dry.

 

 

open the hood, and check the harmonic balencer for wobbles. It will be hard to see the wobble with the cut the balencer has it in, so look in the center of the balencer by the bolt for the bottle instead or go underneeth the car and look directly above it, had something similer happen to my 4.0 Jeep recently and the balencer was wobbling pretty badly.. a new one fixed the problem