i'm having the same issue as you.
i've found this:
the noise i comming from some component on the mainboard, and its caused when the cpu is on idle mode.
Enter setup and disable the c-state option
You'll see that noise dissapear.
Unfortunatelly, by doing this you are disabling a usefull feature on the new processor wich makes it lower its power consumption and clock speed so it can connsume less power and lower it's tempreature. this feature is called SPEED STEP.
i think it's a mainboard related problem, as i assambled many systems and this is the first time happening (with my own computer )
I'm amazed. Does Intel not learn from previous issues? It sounds like the DG45ID saga all over again (even down to the times the noise occurs and the sort of things that it's associated with). Going by what they did with the DG45ID, users of the DH55HC can probably expect to see a new BIOS version which attempts to work around the issue or else a RMA may be needed if it's still a problem (at least that was the case with my DG45ID).