First Start Up Trouble!
you just put the motor in and you initially described "weird clicking sound towards the motor"...when you turn the key (I read that as a low battery starter clicking sound)
My thought is your + battery cable to the starter may not be on tight since it, along with MANY other electrical connections, just got re-connected. Might want to check that if you already have not
IDK if disconnecting battery and letting PCM reset could also make Opti work or not.....I would think more PCM fart or corrupted intermittent connection somewhere.
and on corrupted wiring...you mention aftermarket alarm system....those can play havoc if that wiring gets FU or that alarm brain shiats itself.






