Strange double ringtone for Dial(SIP/105,60,Tt)

Hi i have a number of SIP users and a simple working PRI card setup so when a DID is called inbound, a SIP extension is dialed. My config is below:

[general]
static=yes
writeprotect=no

[globals]
TRUNK=Dahdi/g0
TRUNKMSD=1

[outgoing]
exten => _8./106,1,Set(CALLERID(all)=012221300)
exten => _8.,n,Dial(${TRUNK}/${EXTEN:${TRUNKMSD}}) ;if we dial 8, includ extension DID (if any)

exten => _9.,1,Dial(${TRUNK}/${EXTEN:${TRUNKMSD}}) ;if we dial 9,
; send to trunk

[local]
exten => _1XX,1,Dial(SIP/${EXTEN},30,Tt)

exten => _1XX,n,HangUp()
exten => 600,1,VoiceMailMain()
include => outgoing

[from-pstn]

exten => 12221300,1,Queue(Operators,Tt)

exten => 12221305,1,Dial(SIP/105,60,Tt)
exten => 12221305,n,Hangup()

exten => 12221306,1,Dial(SIP/106,60,Tt)
exten => 12221306,n,Hangup()

The strange thing is i can hear two sets of ringtoneā€¦ both the normal telco ringtone and the SIP extension ringtone. Any idea why this is, what i am doing wrong, and how to fix it? Apart from the above, i can make and receive calls and conduct normal conversation with good quality voice.

Many thanks in advance,

Chris

Does adding an Answer() line before you do your Dial to the SIP phones for inbound calls change anything?