The Iron Duke will vibrate noticeably at idle, as will any 4-banger.
Ever wonder why women love to ride on Hogs with those two huge cylinders and all that vibration…oops, I digress.
The reason you didn’t notice it before is just as likely that, now there is less fluid slipping past old seals and valves, the looseness of the clutches, slipping torque converter and other stuff.
So, just slip into neutral at the stop light and save a slight amount of wear and some gas, because it takes less power to idle in neutral.