Vacuum Leak

[Santa_AK]

Need some help. Have a 2005 PS6.0 and have replaced the electric vacuum pump but am still having the defrost come on when switching to 4wheel drive. Could someone tell me where to start tracing down a vacuum line leak?

Also, while driving, I'm hearing a whine/whistle when letting off the accelerator. I was told it was the turbo and it was normal, but it only started in the last few months, not when I bought the truck. Any ideas what it might be? Any help would be greatly appreciated.

[karmbrown]

It is possible that the vacuum seals in the steering knuckles are leaking.