Ok the Car - 85 Z28 LG4 9.5:1cr with T-5 non CC Canadian Carbed motor only has 90K miles
Mods:
DR rods and adjusted idle mixture
distributor was resprung with MSD light blues
msd cap/coil/rotor/wires
bosch plat plugs (regular)
Mobil 1 15w50 (also did it with 5w30 if that makes a diff)
L69 AF/housing and K&N
Aluminum Radiator
180* T-stat
Complete tune was done new belts hoses T-stat (ignition was replaced 5K ago)
base timing is set to 6*
Dynomax catback
94 Octane only

here is the problem it starts up fine and idles very smooth (as it should with a **** cam) no noise, but once it has come to operating temp when under load at 1/3 throttle and 2/3 throttle it makes this really bad metallic rattle (knock?) if I go to 1/2 throttle it will most of the time go away, and then I have to ease it into WOT, if I mash it while it is rattling it rattles very loud and loses power. RPM doesn't make a diff either, it can do it at 1500 2250 3500 4000 in any gear, no difference.

Im thinking of trying the spraying water in the carb, to clear out any carbon, is there anyother way to do that without water im a little hesitant on that one, and I will check the plugs, could the bosch be running too hot? they where replacement plugs.
Also forgot cat is stock, and in need of replacing could it make this kind of noise?

any help or things to check would be appreciated.