What you are hearing sounds like you are describing my '17 Tahoe. Have had it at the dealer several times. First time they replaced the heater fan motor. No change. They then decided it was the A/C compressor. No change. Then they kept it a few days and still no fix. I then found a Service Bulletin saying it was the A/C lines under the hood vibrating. Ordered the bracket they said would take out the vibration. Bracket didn't come close to fitting the lines. After many trips to the dealer, they gave up and said if GM come up with a fix, they will call me. Right! That was 7 months ago. Just before my 3 yr. and 36k warranty ran out, I took it to another dealer. They first said it was coming from the lifters. They then decided it was the injectors and the word they used was "Not Abnormal". They didn't say normal, just "Not Abnormal". They would not even write up a repair order. So, I am still not happy with either dealership or GM. I called GM and they blew it off and sent me back to see the dealer. It will take a pretty good salesman to sell me another GM after no better service and help I have received. If you do find a fix, I would appreciate you passing it back to me. Not sure it will help since I am past the 36k. Oh, didn't mention that when I turn of the A/C, it quietens down. I would think that would give them a clue of some kind.
