So, you are saying that it didn't tick before you went away, but 3 weeks of sitting idle later, it now does? Could be a lifter isn't getting pumped up with enough oil, for several reasons. I'd try a good oil additive (recommendation depends on where you live), change the oil after it has done its work, and it may clear up by itself.

__________________
1986 560SL
2002 Toyota Camry
1993 Lexus