Hi can anyone help me out, bought an old audi A3 2001 1.6 Petrol for a run around this summer and 6 days in its causing problems!

Im getting up to around 4th gear and there is a grinding/ thud noise and it loses power and the transition light is flashing, then it will go and the light will just be constant.
As soon as i have slowed down and re started the car its fine for a while then it happens again.
Its almost like the car is pulling back and as the accelerator goes down it makes a scraping noise (almost like the noise it would make if the brake pads were non existent). the initial pull back is quite violent (like dropping down a gear or two but after that you could continue.

has anyone has the same issue or can help me out with knowing what it is?

Cheers

James