If you don't have a timing light to use right now and your engine is rattling under load, turn your distributor clockwise just a tad (retard timing). Do this just a tiny bit at a time 'til it goes away. If you go too far, well, it will be too retarded---that doesn't sound right for an inanimate object.
SgtDel
aka "Andy"
www.delbridge.net
1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4