As Mike C says, the first thing to do is ensure the firmware is up to date. There were some changes in V1.95 to USB-B which help with many of the previously problematic USB host drivers.
If this doesn’t solve the issue, and you are on a Windows PC, please check out the following article which includes information on possible reasons for the problem and tools to check the system is suitable for real-time audio. https://support.allen-heath.com/Knowledgebase/Article/View/1002
And if all else fails, please contact us using support.allen-heath.com and we’ll be happy to run through your system with you to try and figure out the root cause.
Ok so here’s an update…of sorts.
The firmware was 1.94 so I upgraded it to 1.95.
Previously the desk was only used for recording the direct outs from the GL desk and this time I plugged in the QU to the main PA.
Using the ‘Alt Out’ TRS sockets I found that this electrical buzzing noise was actually coming through the PA but only when the QU-Drive was being read or playing multitrack.
The noise did not come through the headphones socket or the main XLR outputs or the Mix outputs.
This was a slightly different noise and it reminds me of the electrical interference when a phone was placed near speakers.
Now I’m really unsure of what to do. I don’t want to push this venue to use the QU if there are these issues.