Since moving into my house I have been suffering the noisy bathroom extractor fan. It has been on the to do list of DIY jobs but never seemed to reach the top. Yesterday however the sound of the fan changed slightly during spin down and I decided it was time to investigate. What you should do is turn off the mains power to make it safe before you start opening it up. I had the washing machine on at the time and not knowing which circuit it was on decided to take my chances. Upon removing the cover and getting covered in what can only be assumed to be 20 years worth of bathroom dust I noticed the problem. The centrifugal fan had far too much movement on its motor mount or rather the motor itself was loose on its mountings. Removing the fan from the ceiling and peering in through the non-return flaps I found the motor mounting screws. A good few turns to each screw indicated how loose the motor had shaken over time. Reassembling and activating I was greeted by less low frequency vibration/rumble and more of a quieter humming fan. It's not as quiet as a new fan unit would be but its much much better than it has been. I have probably saved myself about £40-50 on not having to buy a new fan just yet. Not getting an electric shock whilst repairing it I class as an added bonus.