FWIW, I have the same smell from my drivers rear wheel area. I've had all my axel seals changed and its still there albeit its only after you stop. Brakes are fine too. The unit under the rear quarter I believe its part of the emissions system for the gas tank or there of.
Sent from my DROIDX using JeepForum
2003 WJ 4.7L LTD Quadradrive * Kolak 3" Catback exhaust with Flowmaster 70 and Magnaflow tip * Spyder CCFL Halo projectors * Raptor 4500k 35watt HID's low beams * K&N Drop box air filter * Bilstein HD shocks * Stillen Cross Drilled Rotors and Metal Matrix Pads.