mwweiss

I suspect you'll find your short antenna is the source of the whistle. I tried two different after-market antennas and the short one without the twists on it whistled in the same manner. I settled on this one http://www.antennax.com/p-5106-gmc-sierra-2500-2007-2015-5-inch-shorty-antenna.aspx Good luck!

My whistling problem is solved!!! The dealer didn't help or find it. As it turns out, the radio antenna caused the problem. I taped everything off attempting to find the source---window, roof joint, fenders, mirrors, etc. I found that the sound didn't change with moving the mirrors or by rolling down the windows. That was the key--if the sound didn't change after the cab was depressurized by rolling down the window(s), the source was outside the cab. In a final test, I removed the antenna and taped over the hole. Success. I untaped the hole and still success. Forget the dealer, I purchased an after-market stubby antenna and my ride has been quiet ever since. The **** dealer never did contact me after driving in and discussing the issue with them. It seems this type of problem wears you down and eventually people either learn to live with the defect or settle for the excuses they're given. I'm happy this is finally resolved and I can enjoy the vehicle even though it took me several weekend test drives and a few hundred miles of driving to diagnose (it was tough to find an area where I could drive high-speed without too much traffic or too much enforcement). Thank you to all who offered suggestions and their own experiences.

I'm having the same problem with a new 2015 GMC Sierra 2500HD Duramax. I've spoken with GMC customer service--they were no help. I captured the noise on my phone and played for the dealership. They said they would have a tech research it, so I'll give them some time, but GMC should have isolated the cause by now with the number of posts and complaints evident on the forums. For me, the whistle begins between 55-60MPH and is strong and steady above 70MPH. If anyone has solved this, please respond. The youtube post is at Thanks!