I have a clean and well-maintained 2003 GX 470 with 171K. All maintenance performed – no leaks, no issues, etc. Recently, it started making a ticking noise when warm. It also had a slight "knock" to the engine as well. I had the lifters adjusted and the PCV was replaced. It's definitely better but not "Lexus-smooth." The mechanic and dealership say it's characteristic of this engine/year. I've read other threads that mention similar issues but nothing specific unless I can't find the thread.  I'