Gidday Mates.
I work on Chev's, GMC's and Cadi's in New Zealand ! the other week had an issue with a Yukon Denali, had a nasty droning in the cabin with the engine running windows up driving or stationary !
Any way long story short , I figured it out, it is the Active Noise Cancellation , I ended up changing the polarity on the front door speakers (swap over the + with the - wires on the speaker)
I could feel a lot of pressure coming from the door speaker , change the speaker polarity so the pressure is going into the door problem fixed !