Clicking noise

I have a 97 Ford explorer, when I try to start it it makes a clicking noise. I think its coming from the battery or the starter. The weird thing is that after I try to start it and turn it off the radio resets.

So I'm thinking it has something to do with the battery or the wires from the car going to the +& - terminal posts. They are kind of coroded snd the battery is about 3 or 4 years old.

Should I get the battery tested to see if it is bad before I look at putting in a new starter? Or is it something else? Like the alternator?

Also is the starter located right next to the battery?

THANKS FOR THE HELP...