the weird behavior began as a thin red line running horizontally across my cinema display followed by what looked like what might expect to see if an earthquake was taking place in the monitor.
On attempting to restart in the normal fashion the "extra fan" kicked in and I turned the machine off.
SInce rebooting there has not been a repeat of this problem.
being SUnday the Marin Mac SHop is closed or Id probably have the machine in the shop for a serious checkup
can anyone tell me what might be happenng ?
Thanks
MJW