especially when noise abatement procedures are in place.
Absolutely nothing to do with noise abatement. I don't know of any noise abatement procedures that cause you to fly level at 3000ft for over a minute (please correct me if I'm wrong).
In this case N216PK was climbing across the path of AA158. ATC realised that there was a conflict and instructed AA158 to level at 3000ft. If this was done at short notice then there would be a rapid reduction of power. AA158 passed just behind N216PK, 1000ft below. That's how ATC earn their money.