I just installed my headers on friday with my already installed apexi N1 rear section and it ran fine. My test pipes finally came on monday and we installed them but now when i get about 2,000 rpms on it it makes a sorta whistling sound and its there again when i have the clutch it and it goes back to idle, it didn't do it until after my test pipes were in. So I am wondering if anyone knows what this is and how I can fix it.