weird knocking noise???

i have a 99 2dr 5spd xj that is not stock but the sound seems like it isn't an aftermarket issue. i have a 5.5"lift 33's and an SYE and some small things.
the noise is hard to explain but its a irreguar knock that seems to be coming from the fromt and has nothing to do with rpm's of the tires or motor. its a knock that never has the same beet but goes for a few seconds (mainly at speeds over 30 or so on and off the clutch.) its a clanking sound like something is shacking between something (comes in waves and will start to rattle load enough that it bugs me. anybody have any ideas nothing is loose and checked my fenders thanks i need direction it has been happening like 4 or 5 months

not sure what you mean by "on and off the clutch", but if you mean you hear it upon disengaging the clutch, and again upon reengaging the clutch, I'd suspect engine or transmission mounts as the application of power will tend to want move engine/transmission.