Oh, should have mentioned: I have a Radwagon 4 that I got in January.

I have what sounds like a similar issue, although I can only hear (and feel!) the click when I'm really pedaling hard, ie up hill with kids on the back.

A mechanic friend noted the bottom bracket was loose, and tightening the bracket helped at first, but the click has returned even as the bracket has stayed tight. I assume this is broken bottom bracket.

The mechanic-friend told me likely the problem was either:

1) The bottom bracket shell had ovalized in the manufacturing process (unfixable but not fatal for using the bike), or
2) The bracket is a lemon--perhaps a ball bearing exploded or something.

I have also been advised by two different mechanics that the problem is not going to result in any damage to the rest of the bike, which, good!

Curious to hear if others have had success addressing any similar problems by replacing the bottom bracket.