At about 140,000 miles and 10 years after it rolled off the lot, my car started having problems with the audio system. One day I got in, turned the car on, and heard 2 distinct pops that seemed to be coming from the back of the car. After searching I finally found the amplifier, unplugged all the harnesses, plugged them back in, and for a while that seemed to work. Then I happened to run into a guy who had a few IS250s and 350s before and knew a lot more than me about the cars. He had the same problem and told me it was from some kind of air flap that the engineers decided to place behind the right rear wheel. Since that flap is made of rubber it deteriorates over time and exposes the amplifier to whatever your tires kick up. I have seen many pictures of people who had the same problems on many forums, usually posting their rusted amps. The solution is to first seal the hole. Do this either with some make shift plastic and silicone sealer if you have it or if you manage to find the part number maybe you can order it. Then simply buy a new or used amp, although used amps have the risk of suffering from the same water damage and that should fix the problem. Here's a link to a ClubLexus forum that I found helpful.

https://www.clublexus.com/forums/is-2nd-gen-2006-2013/867724-found-out-why-our-is250-is350-and-isf-audio-amps-fail.html?fbclid=IwAR18Zw3jrAhxjrsk4pXC_h3aj2NIw6duuL86isfFvdsz5Lpd4Gqhb9fae0g#post9979830