I have had this problem too, on my '06. I assumed (from the greasy lower valve cover) that it was an oil leak from the upper breather cover. Research on this forum led me to that conclusion. It doesn't happen constantly, seems like only after getting on it hard. Been like that for about a year, I'm planning on getting the seals replaced soon, and will report back if that's what the issue was. I also suspect there could be steam leaking from a small crack in the seam of the coolant overflow tank. Hopefully it's not your alternator dying.