Clicking/chirping sound from MBP whenever it's plugged into external display

[dextor]

Sounds like this

http://www.youtube.com/watch?v=0ZAc9o3Z4Dc

Not my video but I have the same problem. It comes and goes, maybe a couple times an hour.
Only happens when I use external display.

Anyone know why?

 

[GGJstudios]

Sounds like this

http://www.youtube.com/watch?v=0ZAc9o3Z4Dc

Not my video but I have the same problem. It comes and goes, maybe a couple times an hour.
Only happens when I use external display.

Anyone know why?

The pattern suggests drive read/write activity, but I don't know why you'd only hear it when using an external display. Strange!