Welcome to the Forum,
I have a 2010 Tahoe Hybrid, which I bought2 years ago, and love it excet for one issue which I have mentioned several times on this forum.
A loud buzzing sound that comes out in hot weather from the brake system while in AUtostop mode.
After taking my vehicle to the local dealer, and having them run several tests using Tech 2, and making sure all the software and components are up to date, they managed to duplicate the sound that is coming out of my vehicle.
It seems the sound is caused by the ABS pump motor ,which they said it is normal on all 2 mode Hybrids.(they even tested it on a brand new vehicle identical to mine that has been papered to have it delivered to its new owner).
They duplicated the sound in front of me using the Tech 2, by going into the EBCM: Electronic Brake Control module Menu, then turning the ABS pump motor ON Manually. The sound came out identical to the original sound but on a much lower level. (They explained to me that the sound level depends on the air and pressure that is stored in the braking system based on the brake usage). The more I use the brakes paddle the more air and pressure is built up in the system and in certain circumstances and when the vehicle goes into auto stop, the sound is heard much louder where the pump motor is working to release the air out of the system. They even managed to duplicate the sound on a much lower level while the engine was running once the ABS pump motor was turned on manually.
They will send the report to the TAC team , but they said there is no issue to report at this stage and that all is normal unless a bulletin or software update becomes available, they will be acknowledged.
I hope GM can find a fix Soon, and manage to update this issue on their vehicle, cause it it is sad and annoying to have such a loud sound coming out from such a great quiet vehicle made.
Looking forward to hearing from you