Hello, problems like these are some of the most difficult we see. If you can hear it clicking, then the starter relay is actuating, which rules out a control side problem, so, you're going to most likely have a problem between the starter fuse and the starter motor, In order to diagnose this you're going to need to have a test light available when the problem is occuring. You'll want to verify that the starter relay is clicking when you try to start the vehicle, then pull the starter relay out of the under hood fuse panel, and check for constant power on terminal 30(they're labeled on the side of the relay), if the relay is clicking and you have power on terminal 30 your problem is going to be either a bad contact in the relay(they're approximately $10 if you want to just go ahead and replace it) or a problem in the wiring between the fuse panel and the starter. At this point you would want to verify there is power on the small wire going to the starter when you try to start the vehicle. If there is power at the starter and it's not engaging you would have a had started, which i've seen pretty commonly on these vehicles. Below I've also included diagrams of the system, the pinout for the starter relay, and it's location.

RELAY-STARTER MOTOR - (IN PDC)

Generally erratic problems like this are caused by a poor contact on a moving part, which in this system is either the starter relay or the starter solenoid not making a good connection. The starter solenoid is part of the starter assembly which has been replaced, so I would replace the relay on a best guess alone due to it's low cost. Generally a wiring issue wouldn't come and go without at least moving the vehicle.