It depends on which V6 engine you have, if you have the GR or GX model (2.0 non MIVEC 170/180bhp then you're looking at getting a new set of 24 hydraulic lifters from the likes of www.camskill.co.uk This is quite a difficult job and will take a good mechanic 5 to 6 hours to do. If you have the GPX or GP model with the 197bhp V6 engine, then you can adjust the tappets, there is a special adjustment tool available from Mitsubishi or again from camskill. There is a lot of information available for free on www.fto-ireland.com reason the hydraulic lifters on the non MIVEC models rattle is that the lifter is essentially a spring encased in a capsule shape, over time they seize and no longer contract. A temporary fix is to use oil of a different viscosity, but this isn't really a long term solution.