hi
i recently had a dead amplifier which resulted in no sound
the tape/cd all functioned as normal but i had no sound at all - no hissing - nothing - before it went i heard a loud crackle and it was gone
mine was repaired by svt services in edinburgh - £285 inc delivery back - quick turnaround
here is a link to my topic - the last post details the amp removal - its located behind the boot padding on the drivers side.
http://www.lexusownersclub.co.uk/forum/topic/94146-uh-oh-looks-like-my-amp-is-gone/
my car is also a 04 plate with 120K
hope this helps