I have a K&N intake, kinetix ssv, xerd long-tube headers and custom dual 2.5" exhaust with a perforated xpipe and 2 universal mufflers. Upon deceleration there is a air-hissing noise from 3krpm-2.5krpm or so. Sounds kinda cool when I let off a high RPM and the needle flies through this range, sounds close to a BOV. Anyway, it's getting kinda old and really sucks when I'm engine braking in traffic and have to deal with it. Any ideas what it could be so I can fix it?

 

hissing is normal with test pips or hfc's. just try your best not to let it bother you.