loud knocking sound around 4500 rpm's....

[five.point.ohhh]

whenever i get up to 4500 rpm's i heard this really fast knocking-type sound....

I think it's maybe my headers hitting up against my starter, could anyone back me up on this or does anyone have another idea?

if it IS the headers smacking my starter, what can i do to fix it?

thanks a ton guys, i realy do love this site, i get SOOO much help here

-nick