Today while I was on a highway, I pushed the gas pedal down pretty quick trying to accelerate from 60 to 70mph. When I hit the gas, the engine hesitated and made a noise that sounded like someone shaking rocks in a coffee can. It only occurred for a moment and then went away. I could not get the engine to produce the sound again, Is this engine knock or something else? Does anyone have any idea what may be wrong? Nothing like this has happened before. I do experience a rough idle now and then. Thanks.

------------------
'99 F-150 XLT SC 4x4 5.4L Auto 3.55LS Tow pkg, skid plates, keyless entry, UWS tool box, Superchip, Gibson pipes w/ Flowmaster 40 series muffler, K&N filter, BFG 265/75/16 All-Terrain TA/KO

 

Classic sound of spark knock. The knock sensor detected, ECM backed off timing, sound went away.