Slight back story:
Taxiing out with 70 people (plus two lap babies) and our aft FA calls up to say there is some strange squeaking noise coming from around the emergency exit row. The forward FA goes back to check and he says he hears it too. It sounds like metal grinding against metal. He also says a lot of the passengers are looking worried.
Stop the plane, call MX and they pretty much laugh at me over the radio and say they have no idea and to come back to the gate. The forward FA calls up again and says the noise is only there when the airplane is moving.
Get back to the gate and two mechanics come on board. Thankfully they are in a pretty good mood about it and are exciting to play "find that sound". We leave the people on while they go back and look around the area the noise is reported from but they see nothing obvious. Unload 70 people (plus two lap babies) and then close up and push back with the two FAs and two mechanics in the back.
Taxi over to the west hardstand (CLT people know what I am talking about) and play NASCAR driver while we do loops around the ramp for 30 minutes while the mechanics pull of the overhead paneling in the back trying to find the noise (which thankfully didn't go away as soon as they got on the plane... there was no way I was going to accept an "ops check good" on this).
After 30 minutes the ramp controller (who has been exceedingly helpful and keeps asking if we found the noise yet and asked for pictures of the back end of the airplane all torn apart) lets us know that the next outbound bank is going to start in about 15 minutes and we will have to stop driving in circles soon. Thankfully at that time the mechanics think they have found the noise and are ok for us to taxi back to the gate.
So we head back and park. They re torque a clevis bolt that holds one of the overhead bins in place and lube it up.
We load 70 people (plus two lap babies) back on the plane and taxi out (again).
The noise does not return.
Mechanics: 1
Strange airplane noises: 0