Turn the a/c on. Go outside. Turn the power off to the outside unit.
Go inside to see if the noise is still there. If it is, there may be duct issues when they changed the coil. If not, the scroll compressor is the answer.
Vibration limiters could be put on the outdoor unit to make the noise tolerable.
I did see this once..... we tried everything to quiet a unit down. Turns out that the condenser fan motor was the culprit. Had a bad bearing causing the noise.
OK, I turned the a/c on inside and then went outside and dropped the breaker to the a/c unit. Came back in and heard no hum noise at all.
Make sure the compressor isn't bolted in to tightly. Perhaps augment the existing rubber mounts with better isolation pads.
Maybe under the condenser feet.
A resonant frequency (a sound that causes something elsewhere to vibrate) can do weird things but, if thats what it is it's easy to interrupt or baffle.
If the sound is coming through the copper there are vibration dampening couplings (braided copper over rubber) but thats just another element subject to fail in the future.
Isolate the lineset from the building. You probably did help it manipulating that bracket. Changing lineset wouldn't change things unless they were run differently. Your oldie didn't have a scroll which is why you didn't used to hear it.
OK, so in addition to isolating the lineset, I stuffed some fiberglass insulation between the lineset and my ceiling. This lowered the noise level to a managable level that I can live with. I surfed a few websites on scroll compressors and ,oddly enough, they seem to indicate that they're suppose to be quieter than others. Anyway, thanks to everyone for all the help. I've learned a lot here the past couple days. Now I'm off to the "indoor air quality" forum to get educated there.