I've noticed my XF making this tapping sound since I bought it (40k+ miles ago). I check my oil every time I fill up with gas and it's never been low on oil but I'm wondering if the tapping has something to do with the very low visc oil that is recommended? I haven't tried anything other than Mobil 1 0W40 but several people have mentioned to me that switching to a slightly heavier oil might help reduce the noise?

Anyone else have any thoughts on this or tried anything that worked to reduce the tapping sound? It doesn't bother me, I'm just curious.