A humming or whining noise at highway speed often points to gearbox or driveline issues. Learn what causes it, which parts to check first, and whether it’s safe to keep driving.
Why Your BYD Song Plus Is Making Noise
A humming or whining sound from the gearbox at highway speeds can be unsettling. In my years as a tech, I’ve seen this most often with gear bearing wear, low or degraded transmission fluid, or differential issues. On the BYD Song Plus DM-i, the e-CVT gearbox is tightly integrated with the electric drive unit, so the source could even be a noisy motor bearing transmitted through the gear train.
