KONNMAN

I have a 2003 Express. 86,xxx. Went to go start it and do antifreeze flush and it wouldn't start, battery died. I had not started for about week. I jumped started it and it fired right up. As I get to buddys house I shut it off and everything was closed and I started hearing a buzzing/humming sound coming from the drivers side fuse box. Not sure what it can be. Drove fine. 12 hours later I walk by the van and its still making that noise and started it up no problem. Any one have any idea? I think its the battery but am not sure. Thank you