My girlfriends 2009 Tahoe has been having this issue for the past 3 days. When we first noticed it we had just taken it to wash and clean out and then driving home the radio kept randomly switching between the radio and the auxiliary input. The auxiliary input hasn't worked in years. And then she drove it to work the next day and when she tried to start it up after work it was completely dead. I had just put in a new battery a year and a half ago so I didn't think it was the battery. She got it jumped and we took it to autozone, they checked the battery, alternator, and starter and they all were good. We attributed it to her accidentally leaving a light on or something but it happened again the next day. She got it jumped again and drove it home and left it overnight, now it won't start again. No lights turn on, doesn't click, even the power doors won't work. I have no idea what's going on. Seems strange this started happening right after the radio had the weird spasm where it randomly went back and forth between the radio and auxiliary input though. Any help would be appreciated

 

Check your grounds!

 

Google parasitic drain