Hi everyone

When I start my RST up when it's cold or not been used for a couple of hours it's start making a rattle or knock? For about 1second and then it's fine, engine has had a rebuild last year, is this a common problem? I'm guessing that its maybe the oil just taking its time to circulate round? I have it a oil change but no difference? I only does it when first start up from cold and then it's quiet the whole of the drive, any ideas people?