Yeah I have yet to hear any of the "whistling sound". I am really glad to see that the squealing sound is gone though. It might have been some issue with the motherboard pushing out more voltage the pcu needs due to the auto setting in vcore in the bios. My best option to you is to open up the case, wait for the "whistling sound" and turn off all your fans excapt the cpu fan. And see if the sound is still there. there might be air flow problem?? or it might just be a fan.
Thanks for the advice, but I have already checked this. I'm pretty sure it's not a fan.
I've disconnected every fan except the CPU fan and the noise is still there. The noise does not change if the CPU fan speed changes, so I'm fairly sure it's not that fan either. I've searched around on various forums and seen a couple other users report this problem, so I don't think it's an isolated issue.
I'm wondering if it might be an issue with power supplies made by Seasonic. Users of PSU's made by Seasonic or Corsair have reported the same sound, and reported that changing to a PSU made by a different manufacturer fixed the problem. Some of Corsair's PSU's are manufactured by Seasonic. I have a PC Power & Cooling PSU, some of which were also manufactured by Seasonic. Not that I'm an expert on power supplies, but there is enough correlation for me to suspect that it is the cause.
If at some point in the future I can afford to buy a non-Seasonic PSU, I may give that a try.