1999 Ford Explorer Whats wrong?

Since it has gotten extremely cold here in atlanta, my explorer has been making a noise that sounds like a rattle when I crank it up and it continues while I drive. It's loud some times depending on how cold it is outside. But after it warms up, the noise die down some but is still present. I've had three different mechanics listen to it and gotten three different answers. One mechanic said it was the timing chain just by listening to it. Another mechanic said it was the whole timing kit after only hearing it for a minute and after me telling him what the other mechanic said. And another mechanic said it could by my catalytic converter and that I need a new one. The performance has not changed, and it drives fine. It just makes that noise. What could it be? And it also makes a clicking noise that occurs atleast every five to ten minutes sometimes. The clicking noise usually happens while it's idling.