Need abit of advise after a rebuild had new crank and 4 new sleeves ect car runs spot on but once warm it gets a rattle sounds like top end rattle/tapping so fitted oil pressure gauge and from cold I'm getting around 50psi and when warm iv seen it drop under 20psi and I'm sure I see it nearly as low as 10psi what could cause this it's doing my head in could oil pump be failing when warm the engine runs perfect from cold any help welcome