I received a reply, they have declined my rejection stating that the workshop has assessed the whine as a characteristic of the car and as a result no fault was found.
He apologised for the damage caused and is checking CCTV and if confirmed caused by them, will offer to repair it free of charge.
I have cancelled the appointment I had tomorrow for the vibration/rumbling issue to be diagnosed and repaired, after seeking advice from the consumer rights helpline and I have booked the vehicle in for a second opinion with another dealership, but not until 2nd July!
Another mechanic friend of mine has suggested the noise sounds like a bearing in the gearbox or driveshaft/differential bearing. This is what my gut is telling me too! I would not expect a 4 year old Audi to make such a loud noise from a mild hybrid system that isn’t even working throughout the speeds that I’m experiencing the noise.
The consumer rights helpline has suggested I formally write a letter using their templates and send by recorded delivery, which I will draft tonight, giving them 14 days to respond. Despite this taking me outside of my 30 days short term right to reject, this should still be honoured as I am making the rejection within the first 30 days.
This is going to be a big battle, wish me luck. I have lost all confidence in the dealership now.