Chilliam

Hi guys,
I need a little help with diagnosing a noise. I have an Audi A5 Quattro TFSI 2.0.

If I drive it a little faster (120-130 km/h) for a while and chuck it into a few corners pretty fast I start getting this low rumbling/grinding noise from the front end of the car.

I went to a mechanic and they replaced all four bushes of upper arms, both sides. All were shot (I bought car second hand recently). The ball joints seemed good. There was also a knocking noise complimenting the grinding noise that went away after the bushings.

If the grinding noise starts it doesn't go away until I reach the end of the journey. If I keep the speed under 100 km/h range and don't corner as fast there's no noise at all for the same length of journeys.

The noise is low if I'm just driving along, emphasizes when I go over bumps; especially rutty roads.
Please help because I'm baffled.
Thank you all!