99 ranger knocking sounds

I am getting a knocking sound when I let off the accelerator. The noise seems to be coming from the passenger side of the vehicle. There is also a loud thud and lunge forward sometimes when I am accelerating in 1st gear. These noises are totally random (every 7-10 miles). Could this be a drivetrain or transmission problem?

Do you experience these phenomenon while you are parked with the engine running, i.e. gunning the engine, idling, etc. Does the problem occur when your vehicle is moving while the clutch is disengaged? If it only happens while the clutch is engaged and you take your foot off the acceleratot, there's the probability that your engine is stalling due to too low of RPM.

It only happens when the vehicle is moving, the clutch is not engaged, and I take my foot off of the accelerator.

When you said that the clutch is not engaged, I take it as you have the clutch pedal depressed which disengages the clutch. But that indicates that your drive train was disengaged from the engine. OK, two questions: How is it running with your transmission in high and your foot off the clutch and you release the gas pedal? How does it run with the transmission in neutral, your foot off the clutch and release the gas? It's starting to look like it's a tranny/clutch problem as oppose to the engine.