Depends on the mfg. I think Sundance, for example, is supposed to be coming out with a quieter diverter valve, but I also think they were supposed to have it out by now.
The only difference I saw between our 2003 and the 2004's was the display light was a green tint vs our regular white color, and a new type of jet.
Wonder if they keep their new features a secret until the tubs get introduced each year? Announcing a great new innovation too soon may cause people to put off a purchase now to wait for the new ones. Just a thought.
Brewman