Image found here
In my case, I usually hear buzzing, whistling, or a "pop." It feels like a "bubble" expanding in my head, and then it "bursts." Sometimes it is accompanied by a flash sensation. Unfortunately, I usually experience tinnitus following an incidence of exploding head syndrome.
I also experience sleep paralysis, and apparently the two are interconnected.
I can deal with the exploding head far better than the sleep paralysis.
This is the wikipedia entry.
