Citrix Receiver experiencing intermittent audio performance when connecting to a XenApp/XenDesktop Virtual Delivery Agent.
The sound has been observed to disappear after one minute.
Open the default User Datagram Protocol (UDP) audio ports 16500-16509.
These ports are required for audio to perform correctly.
This occurs due to the required default Audio over UDP ports to be enabled in XenApp/XenDesktop 7.5
Citrix Documentation - Multi-Stream Connections policy settings