I haven't found a single post on this website that describes my exact problem so I'm making a new post.
I bought a 1999 blazer (4.3L V6) about 2 years ago. Normally it starts and runs just fine, but t's always had some kind of intermittent starting problem. About every 3-4 months there is at least 2 days where is will not start. It cranks and turns over but won't start. If you wait about 1-2hrs, it'll start right up and will continue to start every day afterwords until the problem comes back. Sometimes the problem happens after it's been sitting for a few days or sometimes just a few hours. Also, the security light sometimes comes on while driving. The gas gauge also doesn't work, but that's cause it got ran out of gas by the previous owner.
Fast forward to today; took it to the shop to work on the brakes. When I came to pick it up, it started right up even though it had been sitting for about a week.
I got home and after I finished installing a refurbished factory radio, I tried to start it, and it didn't start. I tried one more time and it didn't start. It cranked and turned over about 3 times and then nothing but clicks. About 2 mins later, I hear a crackling noise coming from the fuse box. Disconnected the battery immediately and I don't want to connect it again until I know what the cracking noise is.

Does anyone have any ideas what my problem could be?