Early Media is a feature supported by SIP calls that allows two SIP user agents to exchange media before the call is established. This media exchange usually is in the form of a ring tone that the caller hears. Some examples are in-band tones, progress information and other information messages related with queuing services or call status.
More information about Early Media can be found in Early Media and Ringing Tone Generation in the Session Initiation Protocol (SIP) - tools.ietf.org
By default Early Media is always going to be supported in a SIP integration. This implies that when the SIP network supports Early Media and provides a ring tone it will be reproduced to the user. If the user web client also has a default ring tone for voice calls this means that the caller will hear a double ring tone, one from the Early Media and one from the ring file played by the web client. To avoid this overlap it is important to deactivate ring tone reproduced on the client side.