Jeff08

I have a 2015 Sierra 1500 with 100k mile on it. Last week the truck started making a whine or whirling noise that gets louder as speed increases. As you accelerate the noise gets louder. Pressing on the gas I can hear it get louder even though the tach shows no change in RPMs. I tried cruising at 55MPH and shifting into neutral without taking my foot off the gas and the noise goes away. I can give the engine more gas while in neutral and still no sound. Thinking it is something in the transmission but not sure. Could the tow mode switch have something to do with it? I used it for the first time a couple of weeks ago. Don't think its the rear end or transfer case do to the noise going away in neutral. Any input would be appreciated. Jeff