My car produces a whistling sound when accelerating, what might be the cause?

It could be anything, such as air flow, a loose seal around a door, mechanical resonance, or the brakes. If you slightly apply the brakes, does the sound go away, or does it get worse? Some cars make whistling sounds normally. Sometimes there is a leak at the air cleaner. Some cars make a high frequency sound at around 65 miles per hour because the mechanical resonance was designed to be optimized for freeway speeds. The torque converter can slip rather than engage the engine directly. In that event, the RPMs will be higher than normal and the gas mileage will be lower than normal. Maybe the wheel bearings need to be checked.