For ISP's its not necessarily a matter of what you're downloading, just how much of it. Some top tier ISP's let you have whatever you can fit through the pipe they give you.... others advertise a certain bandwidth, but as soon as you start maxing it out 24/7 they get ticked.
There's nothing you can do to hide it from your ISP, and no legal work around unless your community has free wi-fi or something.