clicking noise 2000 Cadillac DTS on 2001 Cadillac DeVille DTS

I have a 2000 Cadillac Deville DTS. I have a clicking noise under the dash. I have heat and air that comes out of the defrosters and the floor only. Got any clues to what the problem could be and how would I find them to repair them?

Asked by for the 2001 Cadillac DeVille DTS
Yey Its a blend Motor that is going bad. It's a real pain to replace.