grinding/knocking at warm startup.

[ben j]

my vp ss starts up alright completely cold, lyk first thing in the morning, but after iv driven it if i park up for say 10 minits then restart it it makes a horrible grinding/knocking noise. lasts bout 15 seconds. i used to think it was only wen i parked uphill, but its gotten worse and does it on level surfaces too. also struggles a bit to turn over wen its fully heated up...
its got 2500000+ ks, im plannin an enginr rebuild, but not real soon, so i wanna see if its fixable.