Popping in upper abdomen!

Has anyone experienced kind of a popping in the upper abdomen? Nothing like a baby kick. Kinda feels like my uterus or something just randomly buldges out. Not that it really is but that's how it feels.. It doesn't hurt but it startles me. It usually happens when I'm in the middle of trying to sit up. I know it's not her kicking because she still kicks really low below my belly button. This popping sensation happens right about the same level as my belly button. I know she's fine in there because she is still active. Just wondering who else has experienced this.. I'm 22 weeks and didn't feel this at all with my first.