Single click when trying to start, is it the relay, solenoid or starter?

This is a random problem. I can go for weeks and the truck will start fine on the first try. Other times I might have to try 5 to 10 times before it will start. When it does not start I get a single click but the lights stay bright. It has a new battery that was put in to "fix" this problem. One other strange symptom that I have noticed is when using the remote to lock the truck the horn sounds very very weak.