Elbow "popping" during workouts and question regarding weight gain

After a few reps of push-ups, my left elbow gets a sort of popping sensation (kinda like when you try to crack your knuckles but they don't fully crack, but almost do [hopefully that makes sense]). It doesn't hurt or anything but it's somewhat disconcerting. I remember a couple people in my PE class would get the same thing when we were on the weight machines so is this something that I'd need to have checked?

Also, how much weight can you put in a month? I don't mean by gorging/binging or anything like that, but by exercising and eating healthy. I'm trying to pack on a couple pounds and it'd be nice to have a number to compare my results to.

Sometimes duing pushups, but mostly during dips, my left forearm muscle will move around like it's slipping. Never hurts, but weird. When that happens, I just finish the set and then stop doing them

Hopefully someone may have seen their physician and have an answer

Hopefully not, my whole body creaks when I exercise but I've spent years being really inactive. For me I pop and crack a little when I start but then it stops. I dunno though.

I hate it when that happens.... :/