Ok well first up i dunno how help full you guys are gonna be because its an after market exhaust (apparently a blitz 2.5" system) however its normally a pretty quiet car. Went for a bit of a hill climb last night and as i was going up the hill it started getting louder, got to the point where it sounded like i had no exhaust on the car. Got to the top and gave it a bit of a rev and it sounded normal. Went back down and the car was screaming again, mainly when on boost. About an hour later driving on the street i got up it and it sounded normal again, what the heck is going on. Car is a jspec s5 so yeah, any ideas

 

i think maybe what you were hearing was your exhaust reflecting against the mountain face. other than that i can't think of anything except for thermal expansion of the exhaust at the flanges during load like when going up or down a hill(assuming you did it the "fun" way using the engine and not the brakes) causing a leak in the exhaust.

my .02

 

Someone else tried to put it that way but no its not the sound reflecting. This is gonna sound weird but the exhaust on my car doesn't sound like a normal rotary, more like a really loud ripping noise its hard to explain. The noise i was hearing was like it had no exhaust at all it was a completely different note it turned into that disgusting rotary noise we all know and love. And yes i did it the fun way i was waiting at the top for 2.5 min for the guy in the supra behind me to get there (it's only an 8k road)

 

Problem solved, one of the nuts holding the dump pipe on had come loose. So when it was boosting and getting hot it was expanding and making it get louder.