Hi my car drives fine with loads of power ,but at the very top of the engine in the centre its developed a rattle ,almost sounds like a loose nut floating about inside,but it gets quieter as the engine gets hotter,any ideas as to what this could be please.?

 

welcome without more information seem kinda hard to identify ,could be a spun bearing or valve knocking ,you may want to take it to the local garage an get another opion