A highway-speed whine from your 308 III gearbox often points to fluid condition, bearing wear, or final-drive noise. Here’s what to check first and when to stop driving.
Why a Peugeot 308 III gearbox can whine at highway speed
A hum or whine that rises with road speed is usually a mechanical noise rather than a simple sensor failure. On the 308 III, whether you have the EAT8 automatic or a manual gearbox, the common suspects are low or degraded gearbox oil, worn input or output shaft bearings, final-drive/differential bearing wear, or uneven gear mesh. In an EAT8, also consider the transmission fluid condition, cooler lines, and mounts; in a manual, check the gear oil level and clutch/gearbox area for leaks. Sensors can log useful clues, but they rarely cause a pure whine on their own.
