Please HELP! 2003 GX 470 Engine Tick / Noise - louder when warm

[GXJeff]

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've noticed that when I press the gas pedal down while idling there is no knock noise and the engine remains smooth, the ticking seems be less severe as well? Can anyone out there give me some guidance? Thank you!

[LonelyHiker]

Many people will say that a tick is caused by an exhaust manifold leak. So that is the first thing to check... Figure out if the tick is louder on the driver or passenger side and search that area for an exhaust leak at the manifold. 

I thought that my GX470 had a manifold leak when I bought it a couple months ago, until I changed the spark plugs... I found that one of the spark plugs was loose almost to the point of falling out. A loose spark plug creates the same kind of ticking noise. The mechanic had started turning the plug in a couple of turns and then must have forgot to tighten it. So you might want to check your spark plugs as well. This GX had always been dealer maintained at Stevinson Lexus of Lakewood, so I know where to stay away from.