What is making my fan relay BUZZ??

Ok. My heater stopped working, and when I checked it, I found that the fan relay was buzzing. I assumed it was bad and replaced it, but the new relay also buzzed. I have now replaced the transformer, capacitor, and the thermostat. Nothing has fixed my problem. The blower motor is getting power, but the capacitor is only getting about 3 MFD. PLEASE HELP!