I have a quite strange 5770. When it runs it creates some a repeated grzzz/squealing sound.

-It is not the fan. I hold the fan still for a brief moment the sound still there
-It is not the temperature, 50 or 60o the sound was still the same.
-It CHANGES together with the core clock! If the clock is 150Mhz, I still can hear the sound but the interval is longer. At 900Mhz the sound frequency increase rapidly. But it is just the frequency of the sound changes; loudness is still the same.

Do you have any idea what is that sound? How to fix it?