I just swap my engine 4A-FE with BT20v.. The problem is,in the morning, when in cold start the engine runs very quiet.. But after the temperature alredy hot, it start making noise like 'taxi diesel engine'.. why?... anyone facing this problem before?.. is it because of the type of engine oil that i'm using?.. (rm55 WIN brand) or my engine got a problem?. any suggestion from all sifus here?...