audio interference

[lfdsteve]

Installing stereo in my 71 firebird resto mod. I have pioneer head, alpine front and rears, 2 10 inch Kenwood subs mounted in trunk with 2 JVC amps and a cap to drive the whole system. battery is trunk mount. All electrical runs directly to battery side posts with exception of head unit which uses original dash wires. All vehicle functions run off separate top posts on battery.
So my problem. It works great when car is off in acc position. It also works great when car is In run position but engine off. This includes fuel pumps fans ect running but not engine. But if engine is running I get a loud pop sporadically thru the system, sounds like when you used to listen to a record album and there was dust on the surface.
Engine is 462 pont with powerjection EFI, coil on cap distributor Acell shielded plug wires.
I am assuming ignition related but its sporadic.
Any thoughts at all?
Thanks
Steve