  We address the electronic resonant transport in presence of a transverse
magnetic field through the single level of a suspended carbon nanotube acting
as a quantum oscillator. We predict a negative magneto-conductance with a
magnetic-field induced narrowing of the resonance line and a reduction of the
conductance peak when the nanotube is asymmetrically contacted to the leads. At
finite bias voltage we study the threshold for phonon-assisted transport.
