dude,
i found this if it's of any help...
ENGINE PING REFERENCES IN OWNER'S MANUAL
Under certain driving conditions, minor engine ping, also referred to as "spark knock", is common for high compression engines such as those used in all Lexus models. Do not hesitate to inform customers of the following information included in their Lexus Owner's Manual:
"If your engine knocks . . .
If you detect heavy knocking, even when using the recommended fuel, or if you hear steady knocking while holding a steady speed on level roads, consult your Lexus dealer.
However, now and then, you may notice light knocking for a short time while accelerating or driving up hills. This is no cause for concern."