OK not to pull the TMI card but:

Im just at 31 weeks today. I went to the bathroom ( #2) and At this point I know not to push too hard if feeling a bit constipated, because of hemorrhoids etc. so I pushed slightly and felt something pop. I can't determine if it was my back or pelvis popping because it was a very faint light popping, and it was inside, but its hard to tell.

Normally I don't tend to worry unless I feel a huge reason to do so, but its not possible to hurt a baby while you're going to the restroom is it?

Also, I can feel him still moving around, and he also got the hiccups about 30 minutes after the incident. So I don.t know, maybe I'm just worrying too much.

Try not to worry, not always easy to do, I know! You will likely hear more pops from time to time. Might be an air pocket, might be from a joint, but you won't hurt baby at all from using the restroom.
Some women will hear or feel a pop sensation when their water breaks, which can be a gush or more of a trickle, but if you are not experiencing any fluid loss, it is likely just one of the many pops and creaks that you may experience.