I have noticed the loud buzzing '''ONLY''' when I am using the '''Sonicare Diamond Head''' Toothbrushes (purchased at Costco) with my Flexcare+ - When I use the regular Sonicare Toothbrushes the loud buzzing stops. I have purchased the Diamond Head Toothbrushes at Costco 3x now and they all do the same thing - loud buzzing. This happens on my 5 year old Flexcare+ and my newer one I just purchased.