If you haven't ordered it yet, get the 14". I just installed my 18" over my lunch break.
When I turned the truck on I almost wept. It's SOOO QUIET! Is it louder than stock? Yes, but at idle it's near impossible to hear it.
That being said, it's a sexy vixen throughout the range. It had a very nice tone, and no drone what so ever. Going up a hill it has a sweet seductive song that tempts you to turn around, and go up the hill again...
I can hear when MDS kicks in, perhaps it's just because with 3.55s and 7500' elevation, my truck is working a lot 'harder' than an equivilant truck with 3.90s at more like 1000'. It's cool, normally MDS kicks off before I even think to shift out of it.
Am I please, very much so. Would I have preferred some more volume, Yes indeed. I will likely go have all the connections welded up. The front clamp SUCKS, and the other 2, well, hell, why not?