hi. i have an 86 4x4 pickup 22r. couple days ago it started making a quick knocking sound in the lower part of the engine, i thought it was a rod knocking so i parked it a few days and this morning i fired it up to move it and it had no knocking at all. so i drove it to work and it ran perfect till i was about there and it started knocking only slightly, on the way home barely knocked at all, but did a little. anyone know what the problem might be? thanks