Mysterious clicks and creaks:
I could feel movement in the crankarm as I pedaled...I tried the eccentric bolts and found that one was loose
Yep, had one of those. There was a slight notchy feeling rather than an audible click.
I have heard people mention clicks from loose chainring bolts...
Yep, had one of those. Funny thing -- I was
sure it had to be the ring on the square taper, as I had recently checked the chainring bolts. So I dismantled both crank arms, cleaned and re-set both, and the wretched click was still there. Just to be sure, I checked the chainring bolts again, and sure enough, one was a little less tight than the others.
I have heard of a seatpost having an audible click inside of a seat tube
Not a click, but a creak on the power stroke of both pedals, on my ti-framed day-ride bike. Couldn't find it anywhere, but my LBS found it when checking my rear der adjustment. Seat post was a little dry.