Seems like you have a conventional furnace and the fact that it is 22 years old - you should be start budgeting for a new furnace.
I know of someone who had a similar problem. His new furnace was oversized, not saying that this is the problems here at all simply because you have had this for so long and I assume that it just started to make that noise.
Maybe time to get an HVAC guy's opinion on this old puppy
