Reasons for the repeating
-One reason can be, as mentioned above, the "wrong" configuration of your audio device(s) in WINDOWS,
while another reason can be the "wrong" configuration of your audio device(s) in Procast, itself.
BUT this is what you have tryed out already, so that is not the case.
I have found another factor, which can be the reason:
Are you currently testing your sounds by running your own stream on your computer?
If so, mute your own stream, cause it causes the repeating sound, getting louder and louder.
Reply if it helps, greetings, gamerexperience