Ive heard loose O2 sensors make a loud rattling noise but not really what you describe. Almost sounds like you some turbo issues as if the wheels are rubbing the housings.

a few posts back there was a video with the sound in question :) link!: http://www.youtube.com/watch?v=WrvhsBGqB9Q

turbo was fine before.. nothing was done to it hmm.. i'll check the o2 but that was also untouched.

Sounds very similar to the noise a fd will make while under boost and one of the metal y pipe gaskets is a little loose between the ypipe and turbos because it isnt tightened all the way, never heard it while revving a car up though.

may have found the problem, i did have the avc removed, must have done a bad job with the gasket.

http://www.rx7club.com/showthread.php?t=665613

will b a week till i find out, time to study for exam week :)

it was the ACV. took care of it yesterday afteroon. so if anyone ever wonders, this is what it sounds like lol. also the acv can be taken out while the rat's nest is left in, no need to remove the rack. use a deep socket 10mm 1/4 drive and a wobble extension. get the socket on the fastner first then attach the wobble. easy. used some tape to stick the bolt in the socket during reassembly.