Bicycle Mechanics - mystery noise

yesterday i started hearing a clanging sound while pedaling my singlespeed. I do not hear it while coasting and it is also not always there. i can't figure out what makes it start or stop. it's driving me nuts

it sounds like something is hitting against something else and has a metallic twang to it. there is nothing rubbing any of the wheels or spokes. chain is lubed and tension is good. nothing feels loose.

i recently swapped a new freewheel and it rained yesterday, could those be contributing factors?

It could be coming from the pedals. Make sure they are tight in the cranks. And depending on the type of pedal make sure everything is tight with the pedal itself.

Pics are always good.

toe strap buckle hitting something?

Do you have fenders on the bike? A rack? Try mounting the bike so you can pedal it; get an old cardboard tube from paper towels or toilet paper and use that to isolate/locate where on the bike the sound is coming from.

Also, check to make sure you don't have a broken spoke clanging around on one of the wheels.

thanks will check pedals and toe straps before riding home. there are no fenders, racks or broken spokes. will also put it on the trainer tonight and see if i can get isolate the sound. i was trying to do it while riding this morning and realized that wasn't the safest way to go. Tell me more about the cardboard tubes, what do i do with those?

i only have a pic from last spring with me right now, (http://img84.imageshack.us/img84/7691/madisonv.jpg) can take some more tonight

Check the length of your laces as well. I had a bike that used to give the occasional series of twang sounds. Took me a while to realize that it was the tag ends of the shoe laces hitting the tubes at certain cadences and when the laces were tied so that the loose ends were longer. THAT was a real headscratcher for a while.

You need to do some detective work, looks like that's your plan. Check all bearings by trying to move the wheels, cranks, headset back and forth, check spokes for loosness or breakage, tighten and lubricate all appropriate points. If you come back having not found it need to know whether when it happens it is in time with pedal rate or wheel revolutions or totally random.

You could improve on the paper towel tube idea. Get a funnel, a couple feeds of plastic hose, duc-tape it to the small end of the funnel, get a towel and duc-tape it to the other end of the hose. Drill a couple of holes in the rim of the funnel, get some elastic, strap the funnel over your ear. Use the dowel to aim the far end of the hose at this thing or that as you pedal down the road.

It could work.

For maximum fun, ride by your boss's house on lawn-mowing day while using this homemade stethoscope.

Not making fun of the paper towel tube. It's a good idea. I'm just having a brainstorm brought on my a couple beers. :)

it started clanking on the way home and i was able to capture the sound with my phone, here it is:

http://www.youtube.com/watch?feature=player_profilepage&v=DRoILykHru0

Spent some time in the garage last night. Long story short: I think it was the 18t freewheel making noise. Swapped it for a 16t and there was no noise. put the 18t back on and the noise returned. So rode in today using the 16t and there was no noise.