* Torque Converter Function: The torque converter acts as a fluid coupling between the engine and transmission. When stopped in drive, the engine is turning the torque converter, which is essentially locked up. If there's a problem within the converter itself (worn clutch plates, internal damage), it can cause a grinding noise.
* Noise Disappears in Motion/Neutral: When you're moving or in neutral, the torque converter's behavior changes. The fluid coupling action reduces the direct connection, and the grinding is no longer audible.
Other Possibilities (less likely, but worth considering):
* Transmission Issues: While less probable given the specific circumstances, a problem within the transmission itself *could* contribute. However, the fact that the noise disappears when moving points more strongly towards the torque converter.
* Driveshaft/Axle Issues: Extremely unlikely to be the cause if the noise is only present when stationary in drive.
What to Do:
1. Don't ignore it: Continuing to drive with this noise could cause further damage and lead to a more expensive repair.
2. Get a professional diagnosis: Take your Windstar to a qualified mechanic or transmission specialist. They can properly diagnose the issue and provide an accurate repair estimate. Describing the noise precisely (grinding, etc.) will help them.
3. Avoid harsh driving: Until the problem is fixed, avoid aggressive acceleration or hard braking.
It's highly advisable to address this issue promptly to prevent potentially significant transmission damage. Ignoring it risks a complete transmission failure, which is a far more costly repair.
