One way to change the vibration mode is to try different propellers. Your airframe/engine combination may be vulnerable to different modes caused by the prop. Even different brands of propeller that are the same diameter and pitch will have different affects.

Also, please be aware that many airframes today have less substantial construction than did airframes of just a few years ago. Also, people are putting larger engines on models originally designed for smaller ones. This is all in concert with the popularity of airplanes that can perform "3D" flight.