360 engine... sounds like diesel engine on light acceleration

Have a 1966 Barracuda that had a 360 in it (mfg 1984). Car just got put on the road (bought as a parts car but decided fix up and put on the road). On mild acceleration it sounds like a diesel engine, sort of pinging?? On hard acceleration or holding at steady speed the noise is not heard. Not sure what the issue might be. Otherwise runs great with plenty of power so don't think it's timing. Any ideas?
thanks-
Claude