i have this exact same problem(among others) and have taken the car to the dealer 3 times now. I try to replicate it with a technician in my car...but of course the damn car would never be that cooperative. Mine usually happens after about 10 minutes of high speed driving on the highway and almost sounds like the little trip meter button is rattling. It's getting on my nerves sooo badly. I'd hate to be a traitor to the IS 300 community, but I am seriously thinking of getting rid of it.