peterwolds

bought the 2.5L wrx 2006 spring this year had no need of heater until a week ago didn't work mechanic had a look the 2 pipes in the engine bay to fit onto the heater matrix were off , fastened them on water dripped into the passenger footwell so disconnected. He got a price for new matrix from Scooby dealer £515 UNBELIEVABLE so I got one from motorads on ebay £107 right one with longer pipes. Took him 3.5 hours to take dash out and fit no problems, warmed car up on driveway hot air at last.
Took car out the next day now have an odd noise as I accelerate I can only describe as a "fluttering " sound - anybody got a clue what it is as didn't happen before and mechanic is back Tuesday to fit top mount/bearing rear strut as a bit noisy going over bumps ?
Thanks for any suggestions