  RX J0440.9+4431 is an accreting X-ray pulsar (XRP) that remained relatively
unexplored until recently, when major X-ray outburst activity enabled more
in-depth studies. Here, we report on the discovery of ${\sim}0.2$ Hz
quasi-periodic oscillations (QPOs) from this source observed with $Fermi$-GBM.
The appearance of QPOs in RX J0440.9+4431 is thricely transient, that is, QPOs
appear only above a certain luminosity, only at certain pulse phases (namely
corresponding to the peak of its sine-like pulse profile), and only for a few
oscillations at time. We argue that this newly discovered phenomenon
(appearance of thricely transient QPOs -- or ATTO) occurs if QPOs are fed
through an accretion disk whose inner region viscosity is unstable to mass
accretion rate and temperature variations. Such variations are triggered when
the source switches to the super-critical accretion regime and the emission
pattern changes. We also argue that the emission region configuration is likely
responsible for the observed QPOs spin-phase dependence.
