I turn the key and get some quick knocks coming from starter area before the starter begins to turn engine over. Number of knocks varies but 5 or less. I suspect solenoid but thought I'd check here before throwing parts at it.
It just passed through my little mind as I started it a few minutes ago, it may be the battery. I'm accustomed to a constant almost buzzing sound in vehicles and they never turn over after they do that. I'm still thinking solenoid though.
Could be any reason, the solenoid would be my last guess.
Check battery, charge and load test, check battery cables and ground wires. You might find one or more issues in that area.