After I have turned the heater on and it warms up and the air starts to flow through the ducts there is an aweful rattling noise coming from the ducts. There is warm air coming out. Is something loose or do I need to call out a professional. Thank you, Mimi

Fan may be out-of-balance if the noise sounds like it is coming from the furnace and not the ducts. If so, you'll need to have it adjusted. Call a heating pro.
Heavy dirt built up on the fins of the blower can cause the fan to be out-of-balance.
If that's not the problem the heating should be able to pin point the rattle.