Clicking noise, Titan won't start. Not battery.

My Titan won't start. I just got a die hard battery less than a year ago. I jumped it and still all it did was click at start up. Days leading up to this sometimes it would be hard to start up and would I have to hold the key for a second or 2 and it would slowly start up. Other times it would take a few clicks and eventually start. I hear the clicking noise best right in the middle of the engine where the thermostat or air duct is. Could it be a relay or the starter? Bc the battery and alternator are fine. Weird... Also my engine has been going it seems and I'm getting a new one soon. Could it be interconnected or is it strictly electrical in this case? Any suggestions would help. -thanks!