High pitch sound captured in Los Angeles on 2 March, 2012.

…found myself in L.A. (CA USA) around 330AM and this terrible noise was filling the night sky. I caught the last of it, but it actually went on for about 25-30 minutes… it was really loud at times and even hurt my head. Seemed like it was coming from all around, maybe feedback from the emergency speakers mounted around this part of town… or was the noise coming from above? Anomaly? Attack? UAO. What is it?!