Yamaha 1300 Tourer - Yamaha 1300 Tourer Fansite

I've noticed this several times. When I start out on my daily commute to work, about 45 miles, I usually stop for gas about 30 miles away and then continue on the last 15 miles. During the first 30 miles, I notice at highway speeds a slight vibration. The windshield is a little buzy and even the seat and foot boards seem to vibrate lightly. After stopping and the continuing the last part, the vibration is gone and the windshield is easy to see through with fine detail. It seems I have to stop first and then continue on for the vibes to end and it doesn't always do it even then. Any ideas?