My 77 L82 4 speed, essentially original, has a somewhat distracting rattle (sort of a clanging) that occurs only when moving and my foot is off the gas. Mainly in between shifts. It is a metallic rattle, and it seems to be coming from the exhaust system. It does not rattle under acceleration (I have had someone listen) and sometimes (rare) it does not rattle at all. Seems to be more prevalent after reaching operating temp. I have had suggestions ranging from the heat riser in the RH exhaust manifold, to a loose pipe (darn if I can find one that's loose), to an obstructed converter. The car runs fine, shifts very true and smooth, and has only about 21,000 miles. Up until my purchase, it was driven about 5,000 miles in the last 10 years, less than 500 miles in the past 5. All regular maintenance has been/is being done. I don't hear the rattle at the carb, linkages or belts/pulleys. However, I am open to any suggestions. It bothers me more than anyone else that rides in the car or listens to the noise. Any ideas?

Have a close look at the pipes as they pass through the transmission cross member. With a little engine flex, they can come in contact with the cross member. ???

Thanks for the tip. I checked and found the pipes to be pretty solid. It has a pretty experienced Corvette owner friend scratching his head as well. One other thing about this noise is that it usually only occurs while underway but with my foot off the accelerator (between gears), however, over 3500 rpm (approximately 75-80 mph) it is pretty consistently rattling. No problem with performance, etc.

Is this rattle under the hood ?

Check shift lenkage?/shifter

Yes, it appears to be from the passenger side, towards the transmission or exhaust. I had the car out today on a fine December afternoon here in Chicago and it did not make the noise as much.

That's what I will check next. Interesting, if I depress the clutch pedal only about 2/3rd's, the rattling is not as bad or goes away. You may have me on to something here. I have a friend who is a whiz on transmisions so he and I will be looking at this soon!
Thanks.

Many year ago, from 1963 especially, the four speed shifter rattled like hell. Some of us just switched to the Hurst shifter. We did not think much about originality then, as Corvettes were usually our single means of transportation, being single and all.

Going out on a limb, but it might be the throw-up bearing going south on you. Had that happen on "The Toy" a couple of summers ago. Swapped the clutch out as well. Nice and quiet now.

Here's another long shot - you said if you depress the clutch, the sound goes away -- or is not as bad??? I know this is not on the passenger side, but how about your clutch fork rattling??