Dear Ruud,
The chief tech at my Lexus dealer, which is Australia's largest, says that in the 10 years he's been there they've never:
Replaced the exhaust system in an LS.
Had to dismantle or do internal repairs to a Lexus V8.
Had to take the dashboard out of an LS (mine had a slight creak, now gone), and
I bought my LS at 100k miles. It had been standing for 15 months and it had a slight exhaust buzz from a tube somewhere in the valley at the rear of the engine. That was replaced and has never returned in 5 years. Perhaps your popping is also a minor item.
Regarding earlier posts, I've owned a Citroen CX, Mercedes 6.3, and a 1985 Jaguar Sovereign, and whilst they each have their virtues, they all had weaknesses. The LS400 however, so far as I've been able to discover, has none.
