Vibrating pelvis?

Jamie • Due with baby #2 in September! A boy!
This morning when I got up I started feeling this vibrating sensation in my lower pelvis. It almost feels like a cell phone vibrating. It only lasts about 5 seconds and stops but has been going on all morning. Has anybody else experienced this? I tried to google and it looks like it could be very common but no real reason as to why it happens or what it's caused by. I go to my doctor today for my monthly check up and will probably mention it then but just wanted to see if anybody else has experienced this?