I'm running Magnaflows. They have a nice burble to them, I've been told they are reasonably quiet and mellow sounding until I get on it--then they open up and get loud. I know they are louder now after a few years than they were when I first put them on. You still need to speak loudly in the cabin, especially on the highway, but it's not obnoxious.
An H-pipe is quieter than separate duals, an X-pipe quieter than an H-pipe.
I lifted the below from an old post about exhaust flow:
Where the 'H' & 'X' pipes come in is to reduce the pressure & pressure waves, both positive and negative, in the pipe by effectively increasing the volume of the pipe. The high pressure wave on one side will typically correspond to a low pressure on the other. By connecting the two, you create an alternative route for some of the pressure waves thus reducing the effect they have upstream towards the valve, plus reducing pressure differentials downstream in the pipe. This is why H & X pipes sound quieter. If you hold your hand on the end of a single pipe while the engine is running, you notice it flaps back and forth: pushed out by the pulse and then sucked back in. This is the 14# atmospheric pressure pushing in to the negative pressure pulse. The crossovers reduce this also.
The main difference between an 'H' and an 'X' is that an H lets most of the actual exhaust gas pulse travel down it's original pipe, while relieving the pressure waves. The X actually takes one pipe and splits it into two. You can hear the difference between all three: individual pipes have a distinct alternating 'thump' from each pipe. An H system will still have an alternating 'thump' but not as distinct--some of the noise & gas will come out the other pipe, but the most noticable difference would be less 'back-sucking' if you hold your hand over one pipe. The X system splits all pulses into both pipes: instead of individual alternating 'full thumps', you get continuous 'half thumps' from both pipes. They sound almost like a 12 cylinder, a soft purring instead of a nasty rumping. That's one reason some guys don't like them. But they do the best job of smoothing out a pulsing exhaust flow.