208 GTi turbo surging under hard acceleration

[manracer]

The child recently upgraded from his 1.2 sxi Corsa to a 208 GTi as his second car. It's a used example from 2016 and has covered 40k. Purchased from a SEAT dealer in march.

It's be fine until today, but he asked me to drive it to hear a knocking noise that it's developed today. It sounds suspension realted.

Anyway more worryingly I noticed it seemed to surge under heavy acceleration, like you can feel it rock you forward and back as the boost comes and goes. It still accelerates pretty well. I also noticed that it seems much less noticeable about say 5k rpm. And when it's going to the red line you can't tell whatsoever.

Any ideas?

Thanks in advance.