Front wheel oscillation I'm not sure if oscillation is the right way to describe this, but when I'm riding at speed (say around 35-40 km/h) and take one hand off of the bars, the bars shimmy or oscillate – kind of like they are resonating with something. It's not bad, but it's new – I'm pretty sure the bike didn't used to do this…

Does anybody know what would cause this? Or better yet, what can be done to eliminate it?

In case it matters the bike is a Trek 620. The front wheel is a pretty plain vanilla rim with Schwalbe Marathon tire (32-622) and a Sanyo dynamo hub.
It seems like it could be:


Loose Hub
Loose Headset
Untrue Wheel
Tire messed up one way or another


From your description, it's hard to believe that the source is in the rear half of the bike (I'm assuming it also happens when you're not pedaling, correct me if I'm wrong).

It seems to be a fairly minor problem (for now at least), that could be very hard to pinpoint.

If you can't find the problem after a technical inspection, I would just keep riding. If you notice the problem getting worse, inspect it again (it'll be easier to find).