It's the transmission still in a REALLY high gear with revs very very LOW while you are going slow. The TCU has not chosen the 'best' gear to be in, rather it has chosen the 'most-efficient.'
Common noise/vibration in fuel-efficient 4-cylinder cars.
To test it, put the GLA in manual mode. Coast along at about 20-25mph, but put it all the way into 6th or 7th and push on the gas, it should re-create that sound
Common noise/vibration in fuel-efficient 4-cylinder cars.
To test it, put the GLA in manual mode. Coast along at about 20-25mph, but put it all the way into 6th or 7th and push on the gas, it should re-create that sound