I have a worrying sound from my 2014 Leaf. When it hits about 56mph there is a thrumming sound from in front of me. It seems to be coming from the engine compartment. It gets louder (even if you don't go any faster) and you can feel the vibration through your feet and the steering wheel. It seems to be particularly loud if the motor is working harder, going up a hill for instance. The only thing I can compare it to is a washing machine when the load is unbalanced. It's very worrying, but once you slow down it goes away and there don't seem to be any effects afterwards. I have had the tyres checked for being out of round and the front end checked out. Nothing. Is it possible something in the motor itself is out of balance? Or has anyone else experienced anything similar? Thanks.