If you are positive it is NOISE and not a air leak noise. Masking tape the front edge on the side window. masking tape around the mirror mount. Tape off the bottom weep hole covers. If this stops the noise, remove each section of tape until the noise returns. If that does NOT stop the noise, MOVE the mirror mount arm outward(you may not be able to use the mirror in this mode. Then see if the noise goes away. If it does, then you will have to experiment where the mirror arm can be set and still use the mirror. Once you find the correct spot, make a small mark so if the mirror is ever moved, you can easily restore the arm/mirror to the correct spot. Also, have you tried driving BOTH ways on the Hiway? Usually, it only makes the noise when you drive one way and the existing crosswind hits and causes the noise. This makes it a little harder to isolate the exact cause. Doug