Periodic ticking sounds like a High Tension discharge or arcing. I can't say I've seen it on the 128 Analog board, but it CAN be a sign of insulation breakdown INSIDE the flyback transformer's windings
You might want to check that the Flyback transformer isn't dusty, dirty or cracked. Clean the FBT body and resolder it's pins.
Check the earth point (black wire with white stripe) at the top left CRT mounting ear (viewed from behind) and the short green earth wire (near the mains power socket) is screwed to the metal chassis.
Check that the folded metal piece is in place at the bottom rear of the analog board. It fits over the edge of the analog board and contacts the chassis on one side and the copper traces on the circuit board and two screws are used to fix the board to the chassis there.