We hear a strange sound during 1-2 sec (it sounds like Asterisk default music on hold) when the call is transferred from Digital Receptionist to Queue.
When transferring calls from an IVR to another destination the Music on hold, as configured under the management console > Settings > Music on Hold is played, so check that you have configured for the MOH under this section.
In this case are you using a supported 3cx VoIP provider? and is there a prompt set in the Queue? additionally does this happen with internal calls or just external?
Does this happen on both external and internal calls, for example, calling an IVR from an internal extension then selecting the option to go to a queue, do you hear the same sound?