There has been much discussion about this at the Yahoo Mainship site over the years. This issue is also noted on the Pilot 34. As with many manufacturers prop tunnels address some issues very nicely. The boats are a little faster because of the lower shaft angle and the semi Kort effect of the tunnel, and the boat saves a few inches of draft, all good things.
In gaining that .5 knot the rule of thumb for prop tip clearance goes out the window, and that's often where vibration issues occur. There has also been some "tunnel burn" reported on some boats.
I do not have a P30, but if I remember correctly Mainship did switch to a 5 blade prop, and several owners of early models went to 5 blade props as a fix. Some also reduced the diameter of their existing props and increased the pitch. Some also installed damping tiles on the tunnel, which is more a bandaide as it doesn't address the core issue.
I'm sure others may chime in, maybe spend some time with the search feature on the Yahoo site, search for tunnels, lots there.