whistle under hood when cold
 

I got an 01 Dakota with the 3.9V6. When the weather is cold i get a whistling sound goin down the road. It will stop if i accelerate or let off the gas. It doesnt seem to effect the way the truck runs its just annoying. Any ideas on what it could be?

its an intake whistle, design of hte intake sometimes makes a whistle sound,
mine does it all the time, sounds like a turbo sometimes

Thanks. why would it only do it when its cold outside though?

different air density,
what actually causes the whistle is the angle of the butterfly valve in the TB, cooler air is less dense so the whistle becomes much more apparent.
your engine might also be trying to pull more air in because of the lower density

i know my air compressors actually work harder when its cold out because it takes more air than in the summer to get the pressure up

Thank goodness it's not just me. I loaned my daily driver to my son and used the Dakota for my commute on Friday. First time on a longer drive in cold weather. I wondered what that darn whistle was.