Passenger side, behind rear wheel well - some sort of sensor?

hmmm, maybe thats whats making that knocking noise.

I believe those are the tire pressure sensors that are transmitted to that from the valve stem. But not positive

I saw it today too when I was doing my rear fog lights. No idea what it is. The tire sensor pressure thing sounds like a good idea.

If it is a tire pressure monitoring sensor (or receiver)... wouldn't there be one for the driver's side as well?

Thats what I thought a first then I remembered that they are transmitted some way but we all should still look in to it cause Im puzzled too.

It must be the gubmint's tracking deevice... logging every time we go 0-60 faster 'n 15 seconds or go over 55 mph!!!:eek:
http://i30.photobucket.com/albums/c314/Z06M16A1/DUBbackSM.jpg

i was thinking maybe a traction control sensor

Answer: Tire pressure trigger module, which identifies the location of the individual tire pressure sensors. There is no module for the left rear as it is not needed. By process-of-elimination, once the system knows the location of the first three sensors it assumes the location of the fourth tire pressure sensor is in the left rear tire.

Damn... we have a smart beast, eh? Thanks for the answer!