popeye2008

Thanks fixmypc,
Yeah you got it, just my luck getting a bad replacement power supply I usually have good luck with Ebay but not this time. I also tried what you suggested with the original power supply not plugged into the AC outlet I still get the hum and I also discovered (which may not be significant) I have to have the phone line plugged into the modem too to get the hum. I only get the hum when I try to use the modem and modem works fine using the battery power alone. it does seem to suggest as you did that it's something to do with the DC jack on the laptop.