I have a 2016 cummins fully deleted with a 5"exhaust MBRP muffler tuned with EFI Live.

My question is that now in NC the mornings are cold and when I crank it up with the exhaust brake on, I hear the high idle kick on but I do not hear the turbo whistle?

The exhaust break still works perfectly when I let of the fuel and sounds like a fighting cat LOL but I have no turbo whistle when the truck is warming up.

Any Thoughts or is this normal?

Thanks in advance for any input.