Courtesy light fuse keeps blowing

I have a 2001 GMC Yukon and for the past few weeks my sunroof and dome lights have not been working. I figured it was just a fuse and I finally got around to checking it and sure enough the courtesy (CTSY) fuse was blown. As I replaced the fuse it immediately blew again, and again, and again. After giving up on the fuse for the day the next time I drove the car I noticed that there is no sound coming from the speakers. The stereo is on and functions normally as far as the clock and station display but no sound. Please help if you can start me in the right direction. Thanks, Ryan