Hi Josh,
A couple of ideas for you...
1) Was the new pulley properly installed i.e., was the front snout of the SC removed and the pulley properly pressed on? I assume the answer is yes, but I have to ask. If it was a "proper" install, it is hard to imagine any damage done to the SC. Whereas if someone tried to press on the pulley without disassembling the SC, all bets are off.
2) I mean no disrespect, but you say that the noise is only occurring at idle. Is it possible that you could be mistaking "normal" transaxle roll-over sounds with what sounds like is coming from the SC? To eliminate this possibility, have someone sit in the car while you are listening to the noise. When you are hearing the noise, have them depress the clutch pedal. If the noise goes away, it is normal transaxle roll-over noise. I hope this is the noise you are hearing which would mean that all is OK!