Thanks Matthias for your prompt response.  I do not know how to set/check "Mac mode".  I have a firewire model and I can only see reference to this mode on the UC model, please correct me if I am wrong.

I donwloaded and installed the latest drivers (3.034).  No difference was made except that now when I play audio I sometimes just get a piercing solid tone.

Thanks again for your feedback.

Well at first I couldn't believe that you were right about my "complete loser" new high spec'd laptop, so I took my setup down to the RME distributers/support techs and they spent a solid couple of hours throwing everything at it.  We were able to ascertain that the laptop architecture just did not support the Expresscard/Firewire interface to the extent that was required for good audio processing. We even plugged in a USB version of FF400, and that annoyingly work very well. So it comes down ultimately to an incompatible laptop.  I was told that laptops like HP and Toshiba were renowned for these sort of problems (due to their proprietary nature), whereas laptops such as ACER and ASUS use desktop style components and as such gave much better results.

Unfortunately this is an expensive lesson.  I wish that the FF400 wasn't such a good product otherwise I would replace it with a USB device. Oh well some decisons to be made now (more money to be spent I suspect)

Hopefully this helps others.

Yes it was the Innovative Music guys. They tested my unit on another computer and it ran fine. Other testing included using different output ports,  Samplitude (changing various ASIO settings) and DPC Latency Checker. Nvidia drivers, network devices, other sound devices were removed/disabled, all having no positive effect.  However on a number of occassions (not every) a solid, piercing tone was emited when audio was sent to the FF, otherwise there was nothing at all..

The DPC checker showed OK (green bars) latency ~250us, but on a couple of occassions showed a red spike.