My 400SB runs great. I have noticed that on deceleration, I can hear and feel a slight popping in my exhaust. It is an internal popping, coming from under the car (muffler???) and not a typical gunshot backfire. Usually occurs when I let up off the gas, and coasting down the highway. The faster I go, and let off, the more harsher the popping gets.
What could this problem be? Should I try higher octane? Do the heads need to be rebuilt? Is it the timing? Any advice or information would be very appreciated.