I just bought a 02 wrx with an ultralite flywheel, brand new stage 2 clutch and sti SS clutch line, I too hear the loud decel chatter/scraping. Previous owner said it started when he installed the flywheel, It also goes away when the clutch is disengaged. I thought it could possibly be the release bearing, but again the previous owner assured me the clutch is mint. Tranny has no issues and shifts amazingly.
Im convinced with kornykidd0.. its notorious and might always be!