I bought mines with that tapping too.Now it taps harder when it's cold,but after 5+ minutes the taps breaks down quit away.
I was concern about that,so i had an isuzu specialist checked it,he said that tapping happens because the VX were sit for a long,long period of time,my VX were storaded for almost 5 years in massachusset before the son of the previous owner's (who died) decided to get rid of it,that's why my VX only had 38K on the clock when purchased on november last year,he also said that will not cause any damage to the engine,neither the engine's performance. I've add almost 5,000 miles since & truefully the VX runs very smooth,it starts rightaway & never give me any troubles so far.
My mech told me to use 5w 20 mobil,but i didn't supposed to add lucas oil stabilizer,however i'll have the VX into the shop as soon fall season shows up to correct that little annoying noise.The tapping is right under the left cover or passenger side.