Thanks for that. I'll look up the manual tonight and recheck the lights. My wife noticed it was on the entire trip one day so I figured it was normal but thought I'd ask.
That's actually not bad! I'm in SoCal too and I've typically been putting in 89 and I'm averaging 19-20 mpg. I don't stomp the gas but I'm not extremely gentle either.
Perhaps I'll tape mine up too as I'm certain that's where the whistling is coming from. I think it's just an edge of the end cap that sticks out that's causing the whistle.
Side note: Sorry to take this off topic but since we're discussing the Signature model I was wondering anyone else with a...
I have a 2019 Sig that came with roof rails and I hear the whistle when I go 50+ as well. After further inspection of the driver side rails I believe it's the end cap that's causing the whistle. I'm planning to bring this up when I go in for my first oil change.