Essen dual-mode-bus diesel / electric comparison

Sitting at the back inside one of Essen's dual mode duobuses on route 145 on a mixed mode journey involving both diesel and electric traction. Note how although when in electric trolleybus mode it is far from silent the motor and transmission noises are considerably more agreeable than the deafening roar of the diesel engine. Also note how when not moving in electric mode there is virtually no noise - unlike when stationary in diesel mode when it is still consuming fuel and polluting both our ears and the air that we breathe. Also heard are the wheels on the loosely laid wooden surface as used where kerb guided buses share trackage with trams / streetcars & the parking of the trolleypoles when the bus switches to diesel mode. btw, the bus stops in the tunnel because it has a red signal - whilst underground the buses interacted with the signalling system, just like steel wheel trains, trams and streetcars.