New head units in old cars: no more noise?

[MyFriendScott]

My '67 came with a pretty nice stereo setup...8 speakers, amp, EQ, head unit, powered sub. It's not going to win any competitions but it's loud enough to drown out someone else next to me playing rap through their loudspeaker in the grill. Anyway...the system has a terrible buzz. I don't even turn the system on any more so I can't remember if the buzz rises with RPM or if it's just constant. It doesn't get louder with the volume so I can turn up the volume and eventually drown out the buzz. In doing research, I learned that I was in over my head in EE terms, something about sharing grounds and my eyes went crossed.

Of course, none of my newer cars have this problem so I know the noise can be eliminated. Do I just need to buy a modern day head unit (one in there now is at least 10 years old) or is there more to consider? The car has an MSD box and 8mm plug wires. Back in the 1980's, those things were notorious for causing noise in stereos. Is that still the case with how these old cars are grounded? Any help appreciated. I'd like to listen to music again in the car. Thanks in advance.

[fbody_mike]

Ive found it has alot to do with which plug wires your running. A carbon core plug wire works best. After that you really have to chase grounds, especially with an EQ and AMP. I have had to add transformer isolators between the head unit and amp to get rid of strange ground issues. You can also try sparkplugs with resistors in them.