I was told by an exhaust technician that the tip can resonate the sound of the exhaust. And from personal experience, using different tips on the same exhaust has made a slightly noticable difference. 2 1/2" tips sounded different than 3" tips. The 3" tips sound slightly deeper, perhaps because the sound echoed more with in the tips. I'm not 100% sure about it, but it's what I've seen and heard. But could an 8" tip whistle more than an 6" tip.... that I don't know. Perhaps you really on heard it when he was getting on it when the boost was up to 15+ PSI. When you have an aftermarket set up you're going to hear the turbo much much more than a stock set up because of how restrictive the stock muffler is. Cat Man is right, straight pipe your rig and you'll see just how much it will whistle while it works.

 

Your wrong man!!

 

i have a buddy w/ a tip that whine pretty good to and at idle. maybe he will buzz in here.

ispeed77 where are you????

he has magnaflow 4" and one of those tips too but looks to be a 5" or so.

 

my truck is a six speed, it has a cat on it.