go on Kazaa. search video files for "1000hp supra"
It's a video of a 1000hp supra on a dyno with a camera pointing at the engine. Listen to the sound, is that the sound you are hearing?

 

its your air intake...when i had my prelude i had a stock intake and then i changed it out with a 4inch intake pipe with k&n air filter and it made a " tssst " sound all the time but got hella loud at 7000rpms....it could be heard a lil bit at idle but only cause the damn thing was so ------ huge.lol....

 

thanks guys for all your answers, i think it may be my manifold leaking air at high rpms and i think i need to tighten it more, it only make it when there is someone in the car with me though, oh well...

 

i have to agree its probly the intake. When i made my intake to a 3in dia intake tubeing and slaped a performance filter on it ,it made a loud sucking noise and when i hit the gas it makes a sweet sound like a turbo spolling up real fast. But I still have that hissing sound i love it scares ricers

 

my car makes that sound to , ive come to the assumption that its a combo of the turbo spooling and a high velocity of air moving thru the system. wicked!