Engine - inconsistant rattle at idle

I have a 1981 Chevrolet V8 267 cid. It has a rattle to it at idle . Goes away when you rev it. I've disconnected the belts and tried it , same thing. Took the fuel pump out and fired it up, the same . Replaced the fuel pump push rod, same thing. The motor has been rebuilt and has good power. What do you think it could be ?

Wrong form. Try here (http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=589).

[QUOTE=cdru]Wrong form. Try [url=http://www.automotiveforums.com/vbulletin/forumdisplay.php?I never used this before.