You running stock exhaust? Does it change or get louder with rpm variations? What have you checked or changed?My engine whistles at all engine speeds including idle. Anyone else ever experience this?
just a thought, when the pipes were replaced the exhaust gaskets may not have been replaced or perhaps not tight enough, when cold more clearance , would equal more noise, when they warm up and expand, less clearance , less noise ? thats where i would start .it's loud as hell when it's cold, i'm thinking maybe something with the throttle body.