Hi Will,
I had the exact same problem that you are describing with my 1999 GS 300 with 127,000 miles. The noise and lights came on and off as I was driving along with a screechy noise from the brake pump. I tried to avoid going to lexus to have it looked at because of the cost but found that no one else could fix it completely and properly. Lexus said that a computer system had gone bad and that caused the antilock brake pump to burn out.
Good Luck with it and if you don't have a warranty, bring your credit card. My bill topped $2400.
