Weird noise coming from my jeep... can't seem to diagnose.

On my way to the gym tonight I was rollin' with my windows down and no radio on. Occassionally when I accelerate, there seems to be a fluttering/vibrating noise that comes from my drivers side front end. At least it sounds that way.

I looked under the hood to see if a fan was hitting any wires. All my wires clear the fan. I checked my center caps making sure they didn't give any on my wheels. The steering is brand new currie's hd. Trac bar is tight. I'm thinking a ujoint might be getting ready to go. Other thoughts?