Perhaps the Wi-Fi signal is being interrupted by interference. This would seem to be the most likely explanation if you are having the same problem with two different iPods at totally different times.
One of my iPod Docks can transmit its signal to other devices, but it knocks out my Wi-Fi signal whenever it transmits. Metal cased devices (such as my microwave oven) can also intefere with the Wi-fi signal. It could even be a something in a neighbour's house. Does the problem continue (as badly) if you are next to your router?