06, P0470 code and high pitched wine at idle

[Thunder101]

I have a H&S with it set at Mild and keep getting P0470 and a high boost (on the gauge) then normal. Im also getting a high pitch whistle at idle .Yesterday I set it back to stock tune and the light has not came back on yet but the whistle is still there. I have it booked into the Ford dealer but would like to know what it might be before they give me some BS. BTW I have done some searching but no one has had this whistle. thx. oh and the p0470 came on first once our weather got COLD
2006 F350 4x4 Crew,egr delete, 3.5" exaust.