Strange Noise When Cold

[DaveK]

I'm not even sure how to describe the noise that has developed on my '03 Sierra 1500HD (6.0). The truck currently has 160K miles and is running strong. But starting back at about 150K, when the truck is cold I get a strange noise coming from the front end at highway speeds...sounds like the "whir" from a helicopter or something. It's not a growl or a rumble. And there is no vibration. It's definitely coming from the engine compartment and isn't noticeable until I am up to highway speeds. After 2-3 miles on the highway it quiets right down.

 

I replaced a front wheel bearing hub that was a little loose, but this noise is still there. Doesn't sound like the tranny. I'm thinking maybe the front diff?? Another possibility I am thinking of is the cooling fan??

 

Anyway, any input on this would be helpful.

Thanks in advance.

[ryank1]

Sounds like the fan clutch to me.

[Motorand]

Any chance it could be a front wheel bearing?