3 beeps under normal driving conditions... No lights?
 

This morning driving to work my 05 manual transmission beeped three times. It sounded like the redline tone. However, I was nowhere near the redline, and there were no warning lights illuminated on the dash? Any ideas? My only idea was that my car was telling me it was below freezing?

Probably your TPMS. Cold tires have lower pressure than warm tires. You should have gotten a light, but maybe it was brief and you missed it, or the light is dead.

Good call. I'll go pick up a tire pressure gauge after work.