bjuice

check your exhaust manifold gaskets and header or exhaust/donut gaskets where it ties into your exhaust pipes underneath your car....this popping sound is typical of cool air being sucked into the exhaust when you let off the gas in return you get a popping sound ..the cool air interuppts the burning off of exhaust gases...


ps..also look over your manifold's or headers and all your exhaust tubing for pin holes..normally it will be toward the motor when this happens...

hope this is your problm..

Brian