My 01 DC 4cyl prerunner has had a knocking sound for the past four years. It only happens when its been parked for 12+ hours, and the temperature hits 40 or lower. I've taken it to several toyota dealers and no one can seem to find anything wrong with it.
The harder you press the gas the faster and louder the knocking gets. Sometimes it goes away in seconds sometimes minutes.
The truck still preforms flawlessly but the sound is terrible.