I have a 2000 silverado ext cab with 5.3. The engine whistles when I accelerate. It doesn't do it at idle or cruising speed. I was wondering if this is normal. The truck runs fine. I think it sounds kind of cool. It must loud enough to hear outside the truck cause one my co-worker noticed it one morning when I got to work. He thought I had one of those throttle body spacers that do make that whistle. As far as I know the truck is completely stock.