I have been using the MBRP 5" system since Aug. 2009, with no droning that I can detect. The only issue that I have had so, far was I needed to install a new TIP on the end. The original TIP fell off on the way to the TDR rally this year. The tail pipe rusted at the TIP joint and the tip broke off on the fine roads in IN.
Whenever I change my engine oil or rotate tires, I check the underside of the truck for leaks or rust. There is some surface rust on the underside of the cab floor but the truck is 12 years old and I do live in the rust belt.