Incoming Calls via CUBE to IVR- intermittent garbled audio

Question

    Connecting via an ITSP and incoming calls are:
ITSP--SIP Trunk-- MyCUBE--SIP Trunk--CUCM--IVR(CTI Ports and RPs)
                                                                        |
                                                                 7900 Type A sccp Handsets  
INbound calls to sccp phones direct sound OK.
Outbound calls sound OK
Inbound calls to IVR intermittent voice quality issues (outside caller hears garbled message)
QoS reservations are adequate and no issues with that (after hours with v low traffic and closed call centrestill have this issue)
CUBE is 3825 and tried 15.1M6, 7 and 2.
All devices and trunk in same region= HQ (tried SIP trunk in Hub_none with same results). intra and inter Region has 64k per call
CUBE has XCode, Soft and Hard MTPs, Conf resources registered with CUCM 8.6
When incoming call comes in via ISDN to CUBE, no issues.
Using G711alaw and G729 r8 in CUBE dial peers. DTMF works fine.No VAD.
Also, when some calls present to agent via IVR, sometimes the agent with 7900 hears silence whilst external caller hears the agent fine. Inbound calls direct to agent DID work 100%. I have noticed on the dead air calls to agent, the ptime = 0 on the handset for Rx... CUBE inbound/oubound Dial peers are matching g711a so I am not sure what is issue.

Answer 1

The problem was solved with the following commands:
network-clock-participate wic 0
network-clock-select 1 E1 0/0/0
modem country v12 belgium
The connections are stable now.
Best regards
Thomas