"Ahhh...so that's what made that noise!" is what I thought when I got to work and discovered the hook was missing from my pannier. Seems that hooking the hook over two bungees that are already hooked to the rack is a good way for the hook to get caught in the spokes and torn off the bag, then caught between the wheel and fender before being lost forever. I had stopped after hearing that racket, did a quick inspection and didn't see the hook was missing. Oh well. At least the sweat on my back was allowed to run freely into my underwear instead of being trapped between my back and my bag like it used to pre-pannier days.