1996 Mercury Mystique Please help! Belt problem?

Please Help If You Can!
I have a 1996 mercury mystique.
I relpaced the altenator and after a week now there is a knocking noise coming from that area. The mobile mechanic came out again and said it needs a timing belt now, although the timing belt looks new, and some gaskets and while he's in there I should replace the water pump and gasket also.
I called the previous owner, as I just bought the car a week ago, to see if he had any paperwork for the car in regards too belts. He had told me about the need for an altenator. He said maybe the mechanic did something to the serpentine belt when he replaced the altenator. I don't know what I should do now? Mechanic said not okay to drive, but I'd like to get a second opinion. Is the serpentine belt idea a possibility?