I just got and put mine in today (yesterday). I went for the Dual Extreme Side Swept (behind both tires) and based on the short test drive that I did after installation, it seemed louder than what I was expecting. So far what I've got is this: When the truck is in park, I hear a slight rumble. At take-off/acceleration, it does get louder and has a nice deep - smooth rumble. Since I don't have any way to put in a sound clip, here's my interpretation of it.
Reving: roARR-lur-lur-lur-lur-lur-lur-lur, roARR-lur-lur-lur-lur-lur-lur, roAR-roAR-lur-lur-lur-lur-lur-lur-lur-lur-lur-lur-lur.....purrrrrrrrrrr.
* notice the smooth-rythmic lyrics of the sound. (sorry, it's 2:30am... I should be sleeping)
On a serious note, the reason why I say it's loud is because I'm comparing it to my muffler that I had on my 2000 4Runner 3.4. I had a Hooker Aero Chamber that had a nice deep tone but was rather conservative.
Rovin's sound clip is excellent and is one of the reasons why I opted for Gibson. It didn't sound as loud as the Magnaflows and it had a nice deep tone at idle.
As for Gibson's customer service, I actually received better service than I initially did from the company I ordered it from. Gibson was more willing to help me and give me immediate answers if I had the information that the middle-man wouldn't give me. (Purchase Order #) Gibson's CS were all friendly and at another time, called me back within 20 minutes when I left a message.
Anyway, PM me this weekend and I can give you a better review/opinion after I do some prolonged driving.