hello all, i have got a problem that for the life of me i cant figure out.
At about 35-40 mph the cab starts to make a whistling noise that sounds like its coming from the drivers side corner where the dash meets the firewall . I don't believe its related to a vacuum problem because in park the sound is not present when I bring the rpm's up to around 2k and the system its self looks sound and works well. However, I figured out that if the a/c is set to the all vent setting the sound goes away. Any ideas?

 

Have a friend help with this.
Get a piece of hose, 3/4 to 1" will do. drive at the speed needed and use the hose as a stethascope and see where the whistle is really coming from. then go from there.
Ray

 

This is why I love these forums. Ideas like that are simply brilliant. I never would have thought of a hose stethascope. Good idea :-)

 

Good call. funny you mention it, a friend of mine just inherited a bunch of old mechanics tools. One of the tools being an actual automotive stethoscope. Ill give it a try. Hopefully ill get to the bottom of the problem.

 

You should throw on a lab coat when you do :-). I never knew those even existed. Cool.