Strange sound

[adough]

My wife has been driving our 91ex. She heard what sound like a stick popping up and hitting the underside. A few moments later she heard it again, and again. It seems to be related to acceleration, whether going up down or level. I drove it around the block this morning, I could not duplicate it. I had to be at work so I didn't have time to get it up to operating temp. When I suggested a belt she said that might be the type of sound she heard but, the belt seems to be in good shape. Any thoughts?
Thanks

 

[Iron Weasel]

Next time it starts happening, have her drive while you ride around with her and see if you can narrow down the area where the noise is. Could be anything from piston slap to loose body molding flapping around. Once you have a better idea where it's coming from then you can figure out what's causing it.

I spent about a week tracking down a noise that only happened once in a while and I had to walk around the block while my wife drove our Explorer around at like 5MPH to figure out what it was. It was the drivers side radius arm bushing that looked fine but was worn out enough that it would only make noise when you went over a bump while turning at the same time.

 

[Rushhour]

I would suggest inspecting at the tranny mount.