When I first start my IS300 in the morning or after it has been unused for a while, the engine makes a knocking sound, almost like a valve or lifter sound, only for about 5 seconds, afterwhich the engine sounds fine. Should I be concerned or is an adjustment necessary?

 

You must realize when your car sits in the garage or wherever it's parked for a couple hours, all the oil drains to the pan. The only oil you have is just enough of a thin coat to keep things lubed when you start up. So yes, this sound is normal...no need to be alarmed.