Well another day of testing and still the problem persists. I thought it could be some of the vst plugins but even if they are not present I still have the busses muting when starting and stopping the transport, in my case the spacebar. I downloaded an earlier version of sonar to test it and the same problem, a pop then busses are pinned and output is muted. HELP!! This is driving me crazy. Everything is up to date, drivers etc. I can change the buffers but that doesn't help. Nothing running in the background that would interfere. CPU is barely moving across all cores.