Toyota dealer couldn’t figure it out after trying tune up, fuel injector service. They sent a recording of the noise with a scan tool to a Toyota engineer and their response was that is normal. I have been using premium gas, tried carbon cleaner in my gas and nothing helps. I’m not an over sensitive driver, the knocking gets REALLY bad when the car is going up a slight hill or getting on the highway via on ramp.
I would suggest using a premium grade fuel from a different fueling station and even go as far as to add some Octane Boost to the gas tank. This would be a good test to determine if it is a pre-detonation issue occurring. It is common for fuel to become contaminated, this is why I suggest changing fueling stations.
Engine Knock Sensor – Pinging Deterrent
The Toyota is equipped with a knock sensor. The Sensor will try to correct the ignition timing if this occurs but is not always as efficient as the human ear. If by chance you think the knock sensor is faulty it can be tested. Using a multi-meter check the Ohms between the two terminal ends on the sensor. Therefore you should see 120 – 280 ohms at room temperature(68-72 degrees). If out of range, replace the sensor.