There are several things that I am going to try. I always shoot tethered but recently acquired an iMAC with a FW800 port, requiring me to purchase an adapter. So my next thing is to go back to my Powerbook and see if it still persists. If so, then I will try a different firewire cable. So we'll see what I come up with.
My main concern was that it is a precursor to something catastrophic, like with a hard drive starts to click. But its more of a nuisance at this point.
Dave