I have had the GTS exhaust for a week now..loving it. No drone at all!
On a scale of 1-10 I would say stock is 4 and GTS is 6 on loudness.
Quality and fitment is great and I also opt for black tips
Current: 2014 M6GC CP and 2015 M3
Past: 2013 M5, 2012 E63, 2011 panamera turbo, 2010 E63, 2010 GTR, 2009 C63, 2008 M5