Ruud 90 deluxe plus, in the last week blower motor noiser

10 yrs ago replaced heat exchanger and burners, changed filter at least every 90 days, more in the winter months in the last week motor ( I'm assuming the blower motor) has gotten louder. Sounds similar to looping diesel motor. I'm thinking the motor is going bad, I've tried to find diagrams of my furnace but have not been successful. 1st question, Does this sound like blower motor starting to fail? 2nd, How hard is this to swap out? 3rd, Where do I get motor?
Thanks for your help,
George
Toledo Oh