Snap crackle pop
 

Hello,
I discovered today an unpleasant metallic snap-crackle-popping sound coming from the vicinity of my rear hub -- but only when I pedal, and even at very slow speeds. Looking through other threads on weird noises, it seems to this uneducated observer that there is likely something wrong with my freewheel. Can anyone tell me how I can determine this for sure? I'd like to do this myself, and not involve any LBSs. My bike is a Dahon Boardwalk with a basic Shimano 6-speed freewheel.

Now, recently I did something that may or may not have been silly: inspired by stories of SS/Fixed bikes, I removed my rear derailleur, selected a gear with a reasonable chainline, and adjusted my rear wheel in the dropouts to get the chain tension right. It's been working fine, but it occurs to me that I might be putting stresses on the freewheel for which it was not designed. Am I worrying too much?

Thanks in advance for any help/insight.

Edit: Even if this is freewheel trouble, is there any reason why I can't just keep riding for the time being?

You probably didn't put too much stress on the freewheel but I expect the chain adjustment and alignment with the single cog you are using has changed. The sound may be the chain trying to come off the cog.

That was my first thought too, but the chainline is almost perfect. Any other ideas?

chain tension is too tight.