I would recommend searching the forum for wrx muffler chirp. Back When I had my 2005 RS I needed a WRX muffler for about a month between the loud crappy obnoxious setup I had for my first exhaust mod.. and the stromung setup with borla replicas I ended up getting.. Anyhow.. back then it was much more prevalent to have WRX mufflers from bug eyes swapped to the RS because there was only a year or two in age difference between the 04/ 05 RS and the WRX . It seems that lots of people reported the dual tipped WRX muffler making a chirping sound like a bird. Once the larger single tip WRX came out on the 05, the chirping went away.. the WRX axleback had basically zero impact on my car other then the larger silver tip looked nicer then the little RS one. The chirping was a result of usage on the RS..