In the end, I tracked down my 14 minute xruns to running the SBLive at
44100 instead of 48000.. I wonder if that would help with the OP problem?
Now, is this a bug with jack (v 0.116) or just a design problem with the
SBLive? I know the SBLive runs at 48000, and has to be resampled (or
something similar that I don't understand) to run at 44100, but surely
that shouldn't cause xruns.. The slow build of static before the xrun
now makes much more sense to me!
James