I've got a relatively limited broadband connection (I live miles from the nearest exchange) and from time to time net access (but nothing else) slows to a near crawl.

I know from a bit of monitoring software that the connection is being fairly heavily used which would explain it but I don't know what's using it. There are certainly plenty of things which might (these days there are dozens of apps that will either regularly or infrequently check data or download updates) but how can I find out?

I'm happy to pay (a small amount of) money if needed, though in that case I'd rather it were a recommendation that me just Googling for something.