Hi, If you have a really slow connection 19.2k or 38.8k then it could be Avast. If it's downloading a program update and your connection is a little limp, data flow for other internet apps will slow to a crawl. It could take quite a while for the download so you probably get sick of it within a few minutes and shut it all down. Am I close?
Check if it's performing a program update, otherwise it could be a LOT of things! What processes do you have running?