On my R61, I believe I remember hearing this, but I also remember where I found something that stopped it.
In the Power Manager (The Lenovo one), edit a power plan and disable the 'CPU Deeper Sleep'. See if this makes a difference.
My CPU is a T9300, so newer processors still have it. I'm sure it's actually the motherboard, not the processor. Probably the processor power regualator making sounds when the processor current draw changes rapidly.