PC makes strange noises

Hello,
I recently built a gaming computer, the specs are listed below

CPU: AMD Phenom 2 810
CPU Cooler: Stock
PowerSupply: CM Extreme Power Plus 650W
RAM: Corsair Dominator DDR2 4GB
MotherBoard: Gigabyte GA MA790FX UD5P
Video Card: Sapphire 4890 1GB

The tower is an EagleTech Dragon

Recently I noticed that after gaming for a certain amount of time my computer would heat up. The Temperature sensor that I had placed on the processor heatsink indicates that the temperature is 56 deg C. At this piont in time the noise would start. It is just a continuous beeping niose that is emitted from the internal speaker. Is my computer overheating or iam i just being delusional???