Hi Chris..
This happened to my Mrs Car few weeks back, Its a known issue and eventually the cluster will need replacing, The bad bit is the Cluster will need replacing by Audi as it needs to be matched to the ECU and all the independent Audi garages cant do it and the cost is around £1500 !!
I Have seen a company advertising repair the existing unit for around £300 and this would mean wont need to be matched as already is