Every time the furnace turns on it makes a loud vibrating noise. It shuts off as soon as the heat shuts off.?
There are two main moving parts in a furnace--the fan motor (aka the blower) and the inducer motor (which is a little fan that pushes the exhaust out on high-efficiency furnaces). If either gets gummed up, they can start to get noisy. Check the fans for obstruction or just a heavy layer of dirt/dust. If it is neither of these, or you're not comfortable taking apart your inducer motor, you may have to have someone look at it--provided there's nothing obviously vibrating against the furnace cabinet itself. NOTE: since the noise stops when the heat stops, that should rule out the blower--that generally keeps going for a few minutes after the burners shut down to cool off the heat exchanger. Turn the summer fan on to confirm that it's the fan and not the inducer motor.
There are only a few moving parts on a furnace. The problem is one of the motors or the blower wheel is out of balance.
It sounds like it may be in your fan motor. You might have a bearing going bad, the wheel could be out of balance, or you may have a loose fan mount. If your thermostat has a fan ON-AUTO Switch then switch it to 'ON' and see if the vibration happens. That will at least verify that you'll need a tech to check out your furnace.
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Check all metal close to the furnace for vibration, it may be the plenum or duct work.
