Help me out here, searched the site and cannot find an answer.

When driving at anything above 30mph and I gently let off the accelerator, I hear a fast clicking/knocking sound (very steady) coming from the engine. As soon as I completely let off the pedal and the truck begins to slow, the sound goes away.

Bad plug? Maybe bad COP?

Just cleaned the MAF.

No other performance issues, nice steady idle, good power etc.

2001 F150
Triton V8 4.6L
Off road 4x4

Thanks for any help you can offer.