Clunking sound when pedalling
 

Been noticing some sort of soft clunk on each pedal stroke.
BB going south?

Or non-drive side crank loosening slightly -- usually one of the other IME.

Drop the chain off the front ring and spin to see if you're still getting the noise.

And what will this diagnose for?

First thing I'd check is allen bolts (or hex) on both cranks if it's a square taper crankset.

Bottom bracket wearing out or loosening would be my next check. Somtimes you can actuall grab both cranks and pull-torque on them and actually see the bb move a little.

However! About 90% of the noises I run into are of seatpost-origin. Try pedaling out of the saddle to eliminate this too. Man, I've had tons of weird noises that I could swear were coming from the crank area or front of the bike but were actually from the seat post.

Why don't you just grab hold of the cranks and pedals, move them around, look for yourself...THEN tell us what you find. You could also check the Sheldon site, as suggested in READ THIS at the head of the forum. Diagnosis when we are not there is much easier if you do just a bit of work yourself.