If it indeed is noise from the valve train it could be tappet noise. Also, it can be caused by loss of pressure in the oil/lubrication system. If the lub system can't pump enough oil up into where the tappets contact the cams it can cause noise in the form of tapping sounds. So that could be the reason why he's referring to oil viscosities.
I'm surprised to hear more motor problems with the VQ. Good luck and let us know how it turns out.
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Always outnumbered, never outgunned.
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