It doesn't just flicker--it flickers furiously.

I realize this can easily be because some update from my A-V or my spyware is being downloaded/installed, but those 2 programs indicate this on my monitor. Ditto with MS updates.

But often there is no monitor indication, period! Just the HDD light all by itself. This could well be due to some process, right?

What are some of the processes and what triggers them--I mean such HDD activity doesn't appear to occur on any regular basis.

Are there other sources of this sudden flickering?