I decatted my 03WRX recently courtesy of a Janspeed/Scoobysport system and now cant help but notice all sorts of noises coming from the downpipe. Seems to hiss and make a metallic type noise as the car spools up. Is this due to the open neck dp or am I experiencing some mechanical failures/leaks etc?

 

"THEY ALL DO THAT SIR"!
Really don't worry mate, it's a characteristic (good IMO) of your open neck downpipe!
I'd prefer if it was louder in mine
JIM