Possibly the amp, I would say so from here. Not unusual though. You could check for a loose connector.
Thanks for replying so quickly, dcfish. Any help / advice you can give will be much appreciated. I have read many postings on club lexus of other "01"LS owners having the amplifier go bad. They have even gone so far as to say the "01" amps are defective and must be replaced with "02" or newer amp. Your reputation preceeds you in regards to Lexus audio systems, and you say these amps do not usually go bad. I have already checked the connections at the amp, removing and reinstalling the 3 plugs. Is there any way to tell if the amp is okay other than replacing it? Could you recommend a supplier for a used amp?
You could bring the amp in and have it tested, I will look to see if I have an amp for your 2001 LS430 UL.