So I know this is a really old thread but it's relevant...
I just installed a MSI Geforce GTX 750 Ti and was really concerned because it was making the same noises--squealing, sizzling, buzzing, squeaking, etc. This occurred mainly when I would run certain games like EverQuest II or run benchmark software (3DMark).
It is not the fan. It's distinctly-electric/frequency sound. Also, I jack the fan speed all the way up to 100% and it was fine.
After reading this and similar threads, I was concerned that it was my 350w PSU (minimum of 400w recommended by MSI). However, I opened MSI Afterburner and lowered the power limit to about 50%, Core Clock to about 40%, and Memory Clock to about 40% as well. Upon running EQII again, the noises continued. I set all the EQII graphics settings to Low and exited the game. Oddly, the Afterburner settings had returned to their default settings. I ran EQII again and the noise was GONE. I turned all the graphics setting up to Ultra and, still, no noise--silent. Also, there are NO PERFORMANCE ISSUES. It's running smooth as silk even at Ultra settings.
I don't know if it was some fluke or what but, to anyone else who has this noise issue, I suggest limiting your performance settings on your GPU, tweaking them until it stops. I hope this helps