Is it significant that my bike sometimes makes a "twang" sound when I hit a bump? I recently bought a 2016 Cannondale Synapse Carbon Disc road bike, which is working great -- however I notice that occasionally when my front wheel hits a bump (e.g. a small pothole or the lip of a driveway), the front fork (or something beneath it) goes into some sort of vibration mode and makes a noise that sounds a lot like the "twang" of a door-stopper for about a quarter-second.

It's a little surprising when this happens (both due to the unexpected sound and the vibration I feel through the handlebars), but I don't observe any obvious problems other than that.

My question is, is this sort of behavior normal/expected with this type of bike, or is it an indicator that something needs adjustment?  (The quick-release lever seems to engaged tightly AFAICT, and there is no reflector mounted on the front spokes)
I would guess these are the spokes. When hitting a bump, you wheel gets compressed. The harder you hit it the more.

When you wheel is getting compressed some (Upper and lower) spokes obviously loose their tension. The wheel then will pop back in it's original shape due the rest of the spokes which are streched. This will bring back the tension to the compressed spokes which usually is noticeable with the "twang" noise. 

It may be a hint that you need to tighten your spokes. The looser your spokes are, the more compressed the wheel can get, which again can loosen your spokes even more. This can create a downwards spiral until the spokes start breaking. Simply check your spokes an tighten them if necessary.

Look I drew a nice picture :)