I have an impression that both noise level and power consumption are not a priority for home network equipment manufactures. After moving to a new house and connecting to another ISP I've got an ISP modem-router which: 1. has a fan and while it's quiet it's not silent 2. consumes around 20 Wt, not much but working 24x7 it would cost around £45/year at current electricity rates.

I think it's technically possible to make a modem which will consume less power and use passive coiling but I don't think they (ISP and device manufacturer) care.