Not sure about Dual Core systems but my Inspiron 630m exhibited exactly the same phenomenon. After (unsuccessfully) trying the workaround with the power management for USB ports, I read about the RM Clock Utility and the ability to enable the “run HLT” command within that program. Once that function was enabled, the noise was gone.
After some additional research I was not completely happy about the HLT command constantly "running" in the background and I eventually abandoned RM Clock Utility in favor of the Notebook Hardware Control (NHC). I undervolted the processor and updated the chipset drivers with files obtained directly from Intel website. I am no longer bothered by the noise.
My wife’s Precision M65, however, is plagued by the same symptoms. I updated the chipset drivers and installed NHC, however did not try to undervolt as, apparently, this is not as straightforward for the Dual Core processors. Hence, the noise remains. Fortunately, this machine is used 80% of the time with the Gentoo Linux and the noise is not present under this operating system.
Interestingly enough, I will have chance to take play with a new Inspiron E1505 today (just arrived) and will keep an ‘eye’ on the buzzing noise. I plan on performing a complete reinstallation after the CDs are delivered (ordering was a completely painless process, by the way, via Dell chat). Will keep you posted.