When my unit was buzzing there was a blockage, the guy that came said it was just a piece of string that was not easy to find, a bit if string trapped somewhere and was stopping the motor from turning, and they were quite cheap, this was there web address, you may have to copy and paste into your browser URL if you can't click it here http://www.advancecare.co.uk/saniflo1.html
Brandon
June 2009