Interesting problem but need more information
 

Hi, sounds like a different problem but let’s try to narrow it down.
1) Do you subscribe to OnStar? If not get rid of it, constantly on all the time as default in the event of an accident. You have to disconnect it from behind and pull the fuse under the hood.
2) Are you having heat issues with AC? A common problem is the cheap heater control module mounted below the blower fan passenger side foot well. When it goes the blower motor still works drawing power. If that’s the issue replace it with the upgraded model which addresses this problem. Might need to change the blower motor at the same time (recommended)
3) The noise under the dash may be your stereo but I don’t think so. If your having heater issues it could be one or more of the heater actuators not resetting properly which makes a clicking noise under the dash.
4) If you have a volt meter and know how to use it conduct a parasitic battery test to see which circuit are drawing power. Both fuse panels need to be tested. If not sure YouTube is a great help or pay a shop to do it for you. Once you know where the power is draining work from that point.
5) Have you ever had a wet floor on the driver or passenger side? Your electrical harness runs under the carpet and could have gotten wet.
I could go on but don’t see the point until you have more info.
Cheers,
Joe

Be Careful pulling fuses
 

Be very careful pulling fuses. There are multiple functions that operate on each electrical circuit. Pulling a fuse might cause other issues. Refer to your owners manual for the location. Never put in a higher amperage fuse than the system calls for. Fire risk!!!

Mark R
 

I have this problem on my 05 h2sut and heard a light clicking under dtiver front behind tire. On the frame is the air suspension relay. Pulled it to check prices and used truck that day. Parked for 18 hours and the next day no battery drain.. Once I find and repair the leak I'll replace the relay and hopefully it continues without draining.. Small leak In passenger rear air I'd noticed weeks before but hadn't traced was causing the air suspension to run after key was off draining the battery.