I have the same issue with an Ideapad 510; are you sure it's not the fan? I've placed several calls to tech support and they have not been helpful at all. Here are several troubleshooting questions:
1)Does the PC make this noise as soon as you turn it on? Does it get worse as you open more windows/tabs in your browser? Please try this and let me know. (I'm just an end-user, and maybe if we work together we can figure this out.)
2)Once you have done #1, go to Settings>System>Power&Sleep>Advanced Options and change the power usage to Power saver. This should theoretically put less stress on the processor. ONce you've done this shut down the machine, wait 5 minutes and then turn it on. Does this resove the issue?
3)Do you have tasks running in the background? Like a backup, or virus scan? You can check this by going to Settings and searching for "Schedule Tasks".
4)As a final check, google the software application "RealTemp." It is a software program that will read the temp of your CPU. Find a trusted source (like softpedia) and download and run it. Let it run in the background and after about 30 mins -- post the result here. What is the temperature range of your CPU?
This is as far as I've gotten. I fear that this might be a design issue with this line of Ideapads. Lenovo doesn't seem to be as good as it used to be!