We have a 2000 Toyota Avalon XL with 25,000 miles on the Odometer. About 6 months ago, we noticed a strange rattling noise coming from the engine whenever we drove the car and reaccelerated. When my mother drives it down the street towards our house, we can hear her coming. In June our Toyota dealer dismissed it as "Pre-Ignition Ping" and said that we should try to change our brand of gas. A month later, after we tried different gas, the noise had not ceased. Since that time, we've been monitoring this noise. The Rattling sound can be heard at 2.5 RPM's and will continue until the RPM's are increased. The engine also sounds louder and rougher at idle than it used to be. We've taken the car back to the dealer numerous times. We've even had the tech drive it to his home while the car was in for service. He still couldn't figure out what the sound was. Since then, the techs at the dealer can identify that ithere is a potential problem, but no one knows how to fix it. We would really like to get this matter taken care of before something major happens to the engine. If anyone has any information reguarding this, please, send it my way :D. It'll be such a huge help. We are all so fed up with the noise, that a speedy service will be the answer to our prayers! Thank You.