2000 Chevy Venture van

2000 Chevy venture van (automatic) with 190,000 miles on engine. “Clunking” noise when accelerating/decelerating as engine/tranny passes up or down through the gears. Also, a “whining” noise can be heard when accelerating, either in gear or in neutral. Rarely happens in cold weather until van has been running for quite a while. Happens regularly in warm weather. If I shut the engine off and wait 10-15 seconds before restart, it usually goes away, but will return indiscriminantly. Tranny was completely rebuilt last year but it still occurs.

Neither the tranny shop nor the Chevy dealer can figure it out.