1990 Volvo 240DL sedan, 152k miles

Okay, I'm puzzled. The car sits for about 3 hours. I get in to drive away and within the first mile I here this repetitive clunking; it sounds like it is coming from the left rear side. The I hear a pop, and the clunking continues.

I stop and look under the rear of the car and see nothing. I drive it home - ~2 miles. I noticed when I was backing up in front of my house I could not hear anything.

I jack the rear up, put it on jack stands, remove the 2 rear tires and look under the rear. Everything looks tight and no missing bolts. The read brakes look to be still okay. This includes the suspension parts, the shocks, and the drive shaft.

After putting the wheels back on, I drive the car around the neighborhood - about 2 miles. Only one time did I hear the clunk.

Not a lot to go on, but any ideas what this might be; what to look for?

I plan to drive it tomorrow for about 25 miles; hoping to repeat it and get more data on what/when it happens.

But any initial ideas might help.

thanks