I have a 1998 6.5 diesel and a couple months ago I got a 4" straight pipe and I love it and sounds great but a while ago I put tint on and didn't roll my windows down for a couple days and when I finally did roll them down I notice that my turbo doesn't whistle anymore unless I get after it, it used to whistle really loud all the time. Is my turbo going bad? Or what is the reason why?

 

Might want to post this in general turbo tech - but I'd first check if your boost gauge is behaving any differently.