exhaust drone/harmonic resonance
Yes the resonating is tuned out with Helmholtz chambers on each pipe at a fractional order of the wavelength / frequency you want to eliminate.
The H pipe btw the exhaust tubes can serve as a dual hemholtz chamber and also connects each pipe together at the same time (I guess).
If you get lucky and arbitrarily or intentionally get the correct length H pipe between your exhaust tubes you help eliminate your resonation in two ways I figure.
This is pretty much the cat's meow, clean setup and bare bones simple too:
http://www.ls1gto.com/forums/showthread.php?p=8617677
Great links and info buck351! Thanks!