Hi @Tze Cherng,

This sounds like High-frequency noise (flicker) issue.

Overclock mainly support for motion display (Games and Videos).

When the monitor is on G-Sync mode, High- Frequency Noise may be observed with Over-clock enabled. This symptom will disappear when Overclocking is disabled.

How to check if monitor is on G-Sync mode:

1. Enter OSD menu->Select “Others”=>Select “Display Info”
2. Check if “Mode” shows “G-Sync” (Figure 18.)

Figure 18. - Adjusting G-Sync Mode

How to check if Overclocking is turned on:

1. Press on “Menu Key “(No.5) to launch following information on screen
2. Check “Overclock” shows “On” or “Off (Figure 19.)

Figure 19. - Enabling Overclock option

How to disable Overclocking:

• Enter OSD menu->Select “Game”=>Select “Overclock” =>Switch from “On” to “Off”

Alienware 25 Gaming Monitor AW2518H doesn't have Overclock option on OSD menu. Would you show me another way to off the overclock?  thank you. 

I can't find "Overclock Option" on OSD menu?