Don't listen to Lexus. They won't help you, they are only interested in selling cars.
I have had this problem and the best place to get a repair done to your amplifier is Supertech Electronics , my repair cost $861 and everything is now working perfect.
Their website is www.electronicrepairs.com.au they are located at Arundel on the Gold Coast Qld. I visited the Gold Coast and had mine fixed while staying there for a few days as they remove the unit and you can still drive away. Other option is to do the test they show on their website and then follow the instructions and remove the unit yourself or get your mechanic to do so. You can then post it to them and they will return it once repaired.
Interesting I have 2 Lexus vehicles and the electronics has played up in both of them.
