How do I stop AM radio frequency interference coming from an AC electric fan motor?

[Zippi]

I just installed a power-vent water heater in my home. It has an exhaust fan that runs whenever this natural gas heater is heating water.

Whenever the fan turns on, I get extreme whining on my AM radio, which disappears once the fan stops. The pitch of the whining seems to be at a similar frequency as the sound from the running fan....there is no doubt, in my mind, that the fan is causing the interference.

FM reception has little-to-no such interference.

Can anyone help me cure this problem?

Thank you for your help!

 

[MensaMan]

I think Radio Shack sells a filter that you can plug the AC of your radio in.

Here's one from C Crane:
http://www.ccrane.com/radios/radio-accessories/radio-noise-filter-surge-protector.aspx