give you the option to mute the modem (normally done at initial set-up) but you can usually access this from your sign in screen.
If not, call your ISP for procedure

It's actually not a good idea to mute the modem. You could have a dialer placed on your machine & a hacker could make phone calls from it.
This happened to me years ago when I got my phone bill with calls from USA to Africa & England. A Virus scan found a dialer!

If you can alway's hear your modem, this won't happen.