Hold Issue on Conference Ph: Whenever a call is placed on hold, phone start ringing out

I've been having this issue with our conference phone for months and no rep is able to fix it. Whenever a call is put on hold, the person on hold hears continuous ringing as if the call is dialing out.

I've been able to set hold music/tones for regular lines but the conference phone doesn't show that option. Has anyone else had this issue??