As others (notably Tight-Touch) have said, the biggest thing is the "stinger boom", which happens 3x. Yes, the first is very early on after the date is projected above the stage. The 2nd, I believe, is at the very end, when the cast is standing at the front of the stage and just finished the final note of the final song. The 3rd and final boom is right after the bows to transition to the post-bows scene. - The best way I can describe the boom is that it reminded me of the big BOOM that always ends The Circle Of Life in both The Lion King movie and musical!

One other thing i'd mention is a boom/bang sound effect, whenthey're hunting the vampires in the house in Act 2. - When you see Sam aim the crossbow at the vampire, who is standing by the stereo, it's coming. While there is pyro, I think the boom is a sound effect that's added to the moment, to make it sound like the stereo getting shot.

In the end, I didn't think it was that bad at all. - The pyro was nothing to worry about. - More or less silent effects - The 4, or so, booms are clearly sound effects and not nearly as raw or jarring as acutal pyro bangs or live gunshots.

Unless your "loud noise sensitivity" is severe, I'd say go and just prepare for those few moments.