Not just old Mopars. This is perfectly normal, "if."
The idle speed might be too high, or the idle mixture improperly adjusted, causing you to have to high idle in order to maintain a decent idle in drive.. Check timing, idle mixture, idle speed, etc
This noise is made worse with an "open" (non Suregrip, or non limited slip rear) because not only must the drivetrain remove slack in the ring and pinion, but the spider gears as well.
