I too am trying to track down a hard to find squeak. Just learned about chassisEar equipment. Seems like it could be very useful!
I've got a few items still to check/inspect to see if my squeak can be fixed without the need for chassisEars.
I did some googling and quickly saw that there are some that have the microphones connected by wire, and some (more expensive) that are wireless. Seems like the wireless ones might be easier to place/test with.
Let us know what you learn and choose and how they work for you. I'll be following....
-Chris