Cant figure out this knocking noise. I have a 2002 gtp. I have ssac headers, 3 inch downpipe, no cat, no res, stock mufflers, 180* tstat, k&n cai, zzp stage 1 throttle body, dhp 1.0 pcm, 3.4" pulley, fuel pump re wire, alt re wire. I have a knocking noise from 2500 rpms to about 4000 rpms. it doesnt do it after 4000 rpms and it doesnt do it before 2500 rpms. i cant figure out what it is. any ideas on what it is or any suggestions how to fix it? please help