1996 Chevy S-10 noises

Something is loose.

If you really think we can tell over a computer, my first guess would be a rusted exhaust pipe clamp. You can see that by crawling underneath and pushing on all of them. If they're okay, try banging on the catalytic converters to see if anything is loose inside them. There are a dozen other things that can rattle but not specifically when letting off the gas.