So I am in the process of sorting out a new-to-me 2003 STR and I have noticed that under hard acceleration there is a ticking noise that seems to come from the driver's side of the engine. It seems to go away when the car is at full operating temperature. Can't really localize where it is coming from any better than that because it only happens under load. Any thoughts on what it may be?

 

Could perhaps be pinking? That happens under load. Could be a hot spot or bad petrol. Hot spots could be spark plugs.
Highest octane petrol for starters and replace spark plugs if no success.
Could of cause be many other things.

 

clogged catalytic converters are known to cause pinking or pre ignition on the STR and XJR 4.2.
it can also be bad plugs or coils or both .

 

Forgive me if these next questions are dumb. I'm familiar with the concept of pinging, but have never experienced it in the real world. Would pinging be steady and linear or random? Also would it get better as the engine heats up or worse? When the ticking starts it is very steady and increases linear to RPMs. I'm running premium fuel, but haven't changed the plugs yet. I'll give that a try.

 

Pinging, pre-ignition, is usually steady and increases with rpm and gets worse as engine heats up.

 

On an automatic it is maybe not that easy, but the best condition for pinking is good filling and slow combustion. Wide open throttle at low rpm.
It might not disappear at high speed, but you can't hear it! If this, it leads to burns and holed pistons, if bad.
If only when cold, it could be piston slap. Sounds terrible, but harmless! Disappears when hot, if not too bad.

 

it could also be a small exhaust flange leak.

 

Cool. It goes away as the engine warms up, so doesn't sound like pinging. Is there a way to narrow down piston slap and what is the fix if that is it?

 

+1 on that.