Furnace works but this morning while running it shakes and sounds horrible. Never did this before. Planning on leaving for the day should I shut off furnace or will it be OK.

It's a Airco (forced air)

In case you need a quick answer until a expert with these shows up, must be something seriously out of balance with the fan motor, pulleys, or the impeller cage, like a broken shaft mount, these are sometimes rubber, or a bad bearing.

Anything causing a rumble like this cannot be good and won't get better, best, if you can, leave the heat off while your gone.

Might be good, if your not fixing it yourself, to get a call today into a HVAC repair firm so you get on the list for after the holiday, if the heat can wait.