Just a little miffed...

My brother and I argue about timing just as I will argue about yours. He runs 32 degrees at full mechanical advance. With the vacuum attached and full vacuum he is at 55 degrees. That is waaaay to high. He argues that it isn't, that the vacuum advance is Mopars way to deliver better mileage. He is wrong. He is too high and so are you. That may give you the noise you are hearing, as valves may be open when they should be closed. That said, fix the timing and put in an H or X pipe. I had rapping on decel and slow accel. It was embarrassing. When I put in an H pipe it went away and I got extra power I could feel.