For the last few rides, I have noticed a random, high-pitched metallic "ping" sound coming from (I think) the front end of my bike. (2009 Specialized S-Works SL2 Roubaix w/ Ultegra 6700 groupset & Mavic Ksyrium SL wheels.) The sound is loud enough for me to hear from the saddle and it sounds a bit like balls in a bearing striking one another when the bearing has no lube in it. The sound isn't regular or cyclical (as if my wheel or crank is striking something). The pings come in irregular clusters and occasionally don't ping at all. The bike has about 2,000 miles on it.
I changed my front wheel out -- but the ping continues with either wheel.
I re-torqued my stem and bar attachment bolts. (They were already at spec.)
I checked my headset -- There's no slop and no binding.
Any ideas on where to look next?