I found a scary CLUNK.
A few months ago, far from home, I heard some scary noises, CLUNKs included,
and they seemed to come from the front wheel. I parked as soon as I could,
hoisted my heavily-laden Wee-Strom onto its center-stand, and tried to find
the source of the noise. It seemed to be coming from the front somewhere.
I had visions of some sturdy piece of front brake detaching itself from the
bike and dangling into the front wheel, thus bringing me to an abrupt and
very painful halt.
I piled coat and helmet onto the pile of gear at the rear, to bring up the
front end. I rotated the front wheel and looked for trouble. Nothing was wrong.
I didn't find the cause of the noise. Everything up front was sound and solid.
You can imagine I was a tad nervous about resuming my ride, but I did just that.
A few hundred scary miles later, I reached home safe and sound.
I unloaded only what I needed for the night, and resolved to find the answer
in the morning. With the bike unloaded, it was quite obvious: the rear bolt
holding the chain guard had escaped, so the chain guard was bouncing around
on the swing-arm and making all those clunky noises. Cost to fix: 20 cents.
I have no idea why the sound seemed to come from the front end,
but I know that acoustics is a complex science, and of course the path
that the noise took was complex. Wearing a helmet makes it tough to
pinpoint a sound's source.
So have a look at your chain guard. It might be the culprit.
I don't really think it is, but you never know. Good luck in any event.