Originally Posted by ucla bruin
So the 2 axle backs, although look the same, are internally different and sound different?
They are 2 different axle backs, both offered by RPI. The GT was introduced first and most hated that annoying tin can ringing sound, so they came out with s second version, the GTM. Visually they look different because the GT has its inlet pipe out of the side of the muffler while the GTM's inlet pipe goes in through the back of the muffler.
PS: Go Bruins!