What is the low pitched whining or whistling noise in your car coming from underneath dashboard that present when engine idle and stops you accelerate?

A low-pitched whine or whistle from under the dashboard that disappears when you accelerate is likely related to a vacuum leak in the car's HVAC (Heating, Ventilation, and Air Conditioning) system. The sound is often created by air rushing through a small opening in a vacuum line or a faulty component. Since it disappears under acceleration, it's less likely to be a belt or bearing issue, as those typically get louder under load.

Here are some potential culprits:

* Vacuum lines: These thin tubes control various functions, including the HVAC system's actuators. A crack, hole, or loose connection in these lines can create a vacuum leak resulting in a whistling sound.

* HVAC blend door actuator: This motor controls the mix of hot and cold air. A malfunctioning actuator might make a whining noise, particularly at idle when the motor is trying to maintain position.

* Vacuum pump: While less common, a failing vacuum pump itself can sometimes produce a whining sound. However, this would usually persist even when accelerating.

It's important to note: This is a diagnosis based on common symptoms. A proper diagnosis requires a mechanic to inspect your vehicle. Ignoring a vacuum leak in the HVAC system could lead to further problems or inefficient climate control.