The click or crack that you hear is a relay switching and, I believe, disconnecting the battery from the system (but not the charge circuit). It's normal.
Edit 1: Going on 3 hours with auto power off = never and uSD card removed. Battery gauge still reads full. I've sent a note to iBasso describing the situation and requesting that they look into it and get back to me so I can pass it on.
Edit 2: Four hours and the battery gauge ticked down one block. I think I'm on to something, here. Going to try a few things to see if I can narrow down what's being read from the card. Not expecting word from iBasso for a while; it's something like 3am there.
Edit 3: After a few more hours of testing it by leaving it idle my suspicion has changed slightly. Rather than the uSD card I now believe that it is the player looking at the .album_art directory on the internal store while a track is displayed but not playing. Going on three hours with the uSD card inserted, all album artwork removed, and the .album_art directory emptied followed by a reboot to make sure everything is clean. Excessive-seeming power drain is still there, less than with 300 or so album covers in .album_art, more than with the uSD card ejected and no music queued. This is still all Mk.I Eyeball measurement so your mileage may vary.
Will follow up with a new post once I hear back from iBasso.
Edited by ratinox - 12/13/13 at 3:53pm