Mine is whitling now that I installed 4" exhaust
I just installed a 4" MBRP turbo-back exhaust on my 2003 6.0L Excursion. It never whistled before, but now it has a high-pitched whistle that almost hurts my ears. It only whistles when my boost gauge reads anything above 1.
Why would I be whistling so loud after putting on a 4" exhaust? It's pretty annoying.