This happens when iPod thinks there is a problem with its hard disk drive, and it is automatically running a disk scan in an attempt to correct the problem. The disk icon with the magnifying glass (with a status bar) is displayed while the scan is running, and the other displays indicate the results of the scan. For an explanation of each, read AppleCare Knowledge Base document #60943.
I'm a passionate, long-time lover of Apple products, and was a civil draftsman and graphic designer before creating the iLounge web site. My prior projects include work for The Los Angeles Times' LATimes.com, and the company Creative Domain, where I developed websites for clients including Columbia Pictures, Disney, Fox Studios, Universal Pictures and Warner Brothers. As the Publisher of iLounge, I direct the site's community forums, photo galleries, iPod User Group, and general business affairs, which have grown under my watch to over sixteen million page views every month. I'm happily married with one daughter, one dog (Rocket the Wonderdog), one cat (Ferris), many iPods, iPhones, iPads, and two turntables.