It suggests that either you have the wrong modem driver installed, or maybe the correct one which has become partially corrupted. Try uninstalling it, and removing the modem. Boot up Windows with no modem insitu, and close down. (Windows will note the lack of a modem at this stage). Now refit modem trying a different slot maybe, let Windows boot up hopefully finding the modem, and then ensure the correct driver is installed. I take it the Modem diags don't come up with any failures?
Failing all that, you can do one of two things. Either unsolder the sounder from the modem card, or do as I have done on many occasions, stick a piece of insulation tape over the sounder orifice - this doesn't completely kill the sound, but reduces it substantially.
ROGER - GØAOZ.