1.
2 Hz does not seem like it would come from the screen. Unless your screen refreshes at 60 Hz and something else is happening at a rate of 62 Hz. Then there might be an interference tick at 2 Hz.
Any combination of events which are 2 Hz difference in frequency, could cause it.
2.
Do you have a wifi card in the computer? Perhaps it is sending out rf pulses at 2 Hz because it is set to detect guests on its network? Can you try turning off your wifi?
Also try disconnecting peripheral devices, one at a time, to see if the ticks stop.
3.
I believe there are sound cards which can detect what device is plugged into the audio 'out' jack.
Suppose that is sending out ticks at 2 Hz in order to detect a device?
Can you try adding a resistor, say 50 ohms, across the plug which goes to your speaker amplifier? This will reduce the amplitude of all signals going to your speakers. But it might tell the sound card to stop the ticks.
4.
A ground loop may be the problem, although that typically causes 60 cycle hum.
I got hum in my system until I disconnected the cable TV. With a little more experimenting I found I only needed to stop the ground rings from contacting. It was okay to leave the tiny center wire connected to the jack.