I have a loud whistling noise starting at about 10mph that either goes away at 20 or probably is drowned out by the engine noise. I can't make it happen at idle or revving the engine up while parked. Happens in forward or reverse. Tapping the brakes or jerking the steering wheel seem to have no affect on it. After truck warms up maybe 10 or 15 min of driving it goes completely away. This noise is very loud sounds like a tea kettle on the stove whistling. Happens everytime I start it up cold when I get close to 10 mph. FYI recently I have had a new gm transmission put in and also a new power steering pump. Any ideas?

 

Vacuum leak. You'll want to check your vacuum lines over.

 

I cannot make it whistle though unless I am moving. I can rev it up to 300 rpms and no noise. It only makes it if I am rolling. Do you still think it can be a vacuum leak?

 

Try higher rpm.may be a condition that only shows under load. It's hard to say without knowing what area the noise is coming from. But your trans swap makes me think along the lines of a line left loose or split.