Volvo S80 high-pitched whistling noise caused by cracked breather box and PCV system issues on Volvo S80

Some Volvo S80 owners report experiencing a high-pitched whistling noise, which may be attributed to issues with a cracked breather box and the PCV system. This noise is often caused by intake manifold vacuum in the crankcase, pulling air past the crank seals due to PCV system problems. Owners have noted that pressing the accelerator can temporarily stop the noise, suggesting a cracked breather box. Additionally, if the noise disappears when the oil filler cap is opened while the engine is running, it likely indicates a PCV issue that requires attention. A cracked breather box can lead to squealing noises and oil pressure problems, making its replacement the recommended repair, especially for older vehicles with higher mileage.