noticed this morning backing out of drive and last few days a grinding noise when braking reversing, fine going forward, car has done 700 miles. anyone else notice this?

Was it humid outside or raining? Was this first drive after being parked?

 

Maybe disc and brake rost dust is causing the noise and should go away after one or two braking.

 

Stone stuck between brake disc and back plate is always a goodun!

if your discs are sitting over the weekend in the rain or wet and have surface rust it will do this, as above it should go away. You might also get this with new pads until they are bedded in.