[reboot]

ISP tech support will NOT help you with this. It's a case of the wrong driver for the modem. Sure, the modem works, but you can't turn the sound off.
Two ways to fix it. Edit the modem install .inf file, and reinstall the modem with the modified driver, or get the correct driver from the modem manufacturer.
FYI, NEVER put "AT" or "=" in the extra settings box. It's redundant, and may cause the modem to quit responding completely. The modem init string is hidden from view, and the "Extra Settings" box is just that...extra settings, not whole ones, that means, settings you want to ADD to the current string, not replace.
Modem speaker noise is a very common problem in XP, and adding M0L0 doesn't seem to fix it in 90% of cases, whereas the correct driver does.
Another case of "Blame MS" for not considering all the stupid things modem makers do to "customize" their modems/drivers.