By default, the first caller in your conference will hear hold music, regardless of whether they dial in with the Participant Access Code or Moderator PIN. The music will stop once two callers have joined your conference, either by phone or via their computer using the Online Meeting Room. This music will also play for those on hold in your Waiting Room, when that feature is enabled.
You can disable the hold music from the Settings page, under Chimes & Name Announce. Just toggle 'Waiting room music' to the OFF position and click save and you’ll hear beeps rather than hold music until the second party arrives.
Note that when you change these settings, any already scheduled calls will not be impacted. Only newly scheduled or 'on-demand' calls will have the new settings applied.
It is not currently possible to change the hold music.