[Troubleshooting] Some kind of squeaking noise when graphics cards are in SLi. What gives?

So a little back story: I put my new system together (thanks to Reddit for helping me with choosing parts.) I had to send off one of my graphics cards (Gigabyte, not Asus) for replacement.

Meanwhile I set the system up and started playing games. with the single card. This never happened while my card was being replaced. I've been on vacation since before Christmas. I have probably put over 60 hours of gaming on the system + spending the first 24 hours running benchmarks and stuff.

Fast-forward to today where I finally got the replacement card. I installed it this evening and starting running benchmarks in SLi. I noticed this squeaking sound when the cards are on full load. It was real bad when I started playing a MMORPG (City of Heroes) and my frame rate became that of a stop motion animation. The "squeak" also applies when running 3DMark2011 and even the Windows Experience Index Assessment! I have an audio of the squeaking noise if anyone needs evidence.

So I ask the minds of Reddit, "What gives?"