I've got a '98 F-150, 4.6 V8 4x4 automatic transmisison. On and off when I'm accelerating there is a loud clonking noise, almost like a tick tick tick. As soon as I let off the gas it goes away. I thought it might be a heater panel that loosened and was moving when the engine torqued but I checked all the panels and they are snug. The noise seems to be coming from the center of the truck...any ideas? Any heater panels that are hidden that I might not have seen?

 

If its only doing it when you accelerate it sounds like it might also be an exhaust leak. Had it happen to my 98.

 

Stop driving it and check all of your spark plugs STAT. That is most likely the infamous spark plug getting ready to launch itself out of the engine taking out the coil with it sound.
Re-torque the plugs to 28 ft lbs. That should take care of that ticking noise. It's about a 90% chance of being the problem. That is of course if it's a ticking sound. Sounds like a small exhaust leak

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