Starting when hot

[Carrmonkey]

At the end of a run my S3 wont restart when hot. Its not always the case but about 50% of the time on restart I just get a clonk from the solenoid which is fixed by letting things cool down or rocking the car in 1st gear

I've cleaned the earth, fitted new starter motor and ignition coil and the battery is ok

Any ideas ?
Thanks
Mark