To start with, sorry it took me so long to get back to this question... I was busy with a client machine.
I see two problems at work here.
1. Your power supply is suffering a slow and silent death as the power distribution systems just can't keep up with the amperage your system is drawing. This is made observable as the 12v voltage drops under high CPU load.
2. Your CPU cores are at an okay temperature, but your socket (it calls that "CPU") is getting rather warm, so your CPU is throttling back its performance to keep the socket from getting dangerously hot. This phenomenon is known as thermal throttling and it occurs when one of two possible situations are happening. The first possibility is that you have overclocked your CPU and it's simply running at too high of a power limit. The second possibility is that your CPU cooler is inadequate. If you have not set overclock settings, then this is simply a cooling issue.
Here is another thing I need to add. Your 970 is (hopefully) hooked up to the power supply via either 6-pin or 8-pin power connector(s) (I'm counting a 6+2 pin power connector as an 8-pin connector). Well those connectors run at 12 volts. What we just observed is that your power supply is lowering the voltage delivery on the 12v rail when running at a high load. The drop in voltage would cause your 970 to destabilize since it draws its power from the 12v rail.
Two things need done here: First, get a new power supply, I will suggest a few below. Second, get a new CPU cooler. If you don't know how to put a CPU cooler on properly, there's a wonderful resource called YouTube, you're sure to find a demonstration video there.
Also, I thought I should add this... When the system halts and the last frequency just keeps looping in the speakers (which causes that annoying buzzing sound), it's usually a problem with the CPU missing a cycle(s).
For a cooler, I recommend the Cooler Master Hyper 212 Evo -
http://pcpartpicker.com/product/hmtCmG/cooler-master-cpu-cooler-rr212e20pkr2
For a power supply, any of the following would work for you - http://pcpartpicker.com/products/compare/cooler-master-power-supply-rs550afbag1us,corsair-power-supply-cp9020090na,evga-power-supply-220g20550y1/ Please note that I personally recommend the Cooler Master V series of power supplies.