I acutally looked into this. Thought it was the valves and they just needed adjustement. Dealership said it is a well known issue from Lexus, and that it isn't the valves, in fact it is the fuel injectors and the rails. Apparently there is an upgrade kit out there to resolve this, but Lexus of course is charging a significant of money. Price wise i cannot remember how much anymore. But basically, its normal and live it is what they said...unless you want to shell out some money for the ugrade kit.
Sorry, here is the link. Can't figure out how to delete the first post.
For your reading enjoyment, here is the applicable TSB for the injector issue.
Cheers.
FUEL INJECTOR “TICKING” NOISE -- EG005-05 Revised.pdf