Hello my name is XXXXX. XXX sound you are hearing is the lift gate module. It sounds like the module has shorted out internally. It is responsible for all your remote function actuation so that explains why your remotes aren't working. It is also possible that it has lost its ground. Sometimes the wires brake in the piece of the harness that flexes when the tail gate is opened or closed. I am going to recommend you take it to the dealership and have it checked since they are the only ones that can program the module once it is installed. They will also need to program all your remotes once the repair is complete. I have seen both problems with these trucks so I couldn't tell which one is more common. If you have any other questions please feel free to ask. Thank you!

I did read your full letter. I think the people at that dealership either didn't hear the noise it's making or just didn't feel like messing with it because it isn't setting any codes and they will actually have to do their jobs. There are places out there that will run off mysterious electrical problems like yours cause they can't make any money on them. To diagnose this problem will most likely be time consuming. If you could get it to make the noise while it was there they will be able to find the problem. I was simply telling you what I have personally seen on your body style truck. I have replaced three of the liftgate modules on Trailblazers in the last year for the same problem you are describing and repaired the wiring on two Trailblazers and four Tahoes for similar symptoms. I do this for a living and deal with these trucks every day. You asked a question and I answered it with personal experience. Just because they didn't know what to do with it doesn't mean I don't. If you are not happy with my experience I will opt out and you can ask someone else's opinion. Thank you.