[joedirt]

Mine do it under heavy braking. It will come and go. It seems to be very common on the H3. You could always replace the front and rear rotors with the slotted and drilled rotors. The stock rotors can warp easy when offroading and driving through water. I had the same issue on my 98 Jeep Wrangler with 36" swamper tires. I replaced them with slotted and drilled rotors and never had a problem after that. I havn't tried it on my H3 yet, but I am sure that it will be better than factory. They generate less heat and do not warp easily. Someone is selling a set on ebay. Also, get some good semi metalic pads and your set. They are well worth the money especially if you have big offroad tires. Goodluck!

http://cgi.ebay.com/ebaymotors/06-07-Hummer-H3-Drilled-Slotted-Drill-Slot-Rotors-F-R_W0QQcmdZViewItemQQcategoryZ33564QQihZ019QQitemZ2 90170472834QQrdZ1QQsspagenameZWDVW