Older and cheaper ballasts are prone to humming and causing rf interference with other appliances. If these are old lights with starters, then you are also using the old style bulbs or else you have a mismatch with the type of bulb and ballast. With starters, just replace the whole fixture particularly around computers. When I've priced good quality ballasts, it is just about as cheap or cheaper to buy a whole new fixture. Also the bulb sockets will go bad over time. Remember cheap $8 shop lights have a cheap ballast. The lesser the quality of ballast, the more trouble they have starting and especially in cold weather and more trouble you have with interference with computers. Also scrape paint around ground screws as a bad ground will cause problems. Keep flourescents lights off of the same circuit as a computer.