Rattle sound behind the dash around the heater core and firewall only when the vehicle is in drive at an idol. No other gear triggers it.

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! That rattle you’re hearing behind the dash of your 2005 Lexus ES330 when it's in drive at idle could be a loose heat shield or a mounting bracket around the exhaust or engine components. Sometimes, engine vibrations in drive can cause parts near the firewall, like the heater core lines or A/C components, to rattle. Since it only happens in drive at idle, I'd also check the motor mounts—they can wear down and cause extra vibration, leading to those pesky sounds. If you need any further advice or want help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554!