I have a '13 6.2 with 11k on it and it's started making a weird noise since the temp has turned cold. At first I noticed a slight whistle at certain rpm's but the temps were around 0 so I didn't think too much of it since stuff gets noisy the colder it gets. Today the temps were in the upper teens and I'm noticing a new sound. From around 1000-1500rpm I'm getting a whining sound that is noticeable in the cab. It's coming form the engine since it does it while sitting and I can make the sound appear by getting the engine at the correct speed. It's louder when the engine is cold but I can still notice it a bit after the engine is at operating temps. Below 1000 and above 1500 rpm there is no noise. Does anyone else notice anything like this on their trucks? I never really noticed it before, but since I heard the slight whining last week I've been listening more and I know that's when you start hearing noises that you normally wouldn't pay attention to.

 

I have the same thing from my 5.4 I think it is the fan clutch, but I haven't narrowed it down for sure.