weired knock/miss im stumped

ok heres the deal with my 99 gt.its got 67k on it. and when ive warmed the car up or drive it for a little, and give it gas more then half throttle. when the clutch is in or neutral only makes a nosie that sounds like your knocking n somthing aluminum, or hittings tools together..i was thinking maybe my tensioner, but it doest do it when i first start the car??? and to the miss now..and doesnt stop when using 93 oct. gas
im in a low gear, and give it gas around (1000-2100rpms) has this miss hiccup thing..only does it once while pressing the gas. and another part of the miss stumble thing is say im crusing on the highway in 5th gear for a while. then throw in the clutch and rev it.. it kinda backfire/stumbles then revs..
i notice the car smells rich when i start it. and so does the engine bay,,car has new ngk v power plugs.. i dont know what to do.. im stumped.
only mods to the car are underdrive pullies "piggy back style" and a jlt intake tube with stock filter. and i have a shifter but that doesnt matter
well i found out what another nosie is lol.. my throw out bearing is nosiey..
but back to the original nosie, another thing wiered is. the car will not make the nosie it you have drove the car.. if you let it sit there and idle.. it will never make the noise..but say im driving and then go to a stop light then rev it, it will then??
i was hitting my cats and noticed ratteling in there, but still doesnt sound like it..im stumped..oh yea..after iv let the car run for a awhile. the idle starts to sound like it has a miss in it..
i am about to burn this car.
 
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I have a rattle that sounds almost exactly like what you're explaining. Couldn't find anything loose, wasn't detonation...etc. Dealer told me it was a busted up cat on one side. The part is on order so I haven't had it fixed yet, but a bad cat seems like a plausible explanation for what I was hearing. My car was rattling in neutral, in gear, but always when revving it up. Wouldn't do it at idle. But did it under WOT, or granny driving...and rarely did it stone cold. So maybe you got a bad cat...especially if you're hearing something rattling in it.