Does the tone disappear if you disconnect PC from the mains supply or if you disconnect the modem? If so, could it have anything to do with the BIOS being set to 'Wake up on LAN' or something similar. Or am I talking rubbish :-))
Thanks Graham. Will give that a go but will not be able to do it until the end of the week.
One thing that occurs to me is that my modem(s) are not plugged directly into the socket. I have a filter plugged into the socket into which I have my adsl and my dial up modem connected. The socket I have is a standard telephone socket and so would not take the adsl modem plug directly. Just wondering if this might be the cause? (no telephone connected on this socket).
Did the ADSL modem not come with a lead/adaptor to connect directly to the phone socket? You will have to include the dial-up modem in the tests as above, so unplug that as well, leaving just the ADSL modem connected (via a filter if you don't have a lead/adaptor).
Also check the cable to the ADSL modem is away from sources of inducted interference. Come to think of it, listen for the tone and then move the cable around. With the PC turned off, the cable may be in an 'unterminated' state, and more prone to induced noise.
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