Sounds a bit like a rockfall to me, perhaps nearby? The slow buildup and slower subsidence of the sound intuitively fits what I would expect for a rockfall, and also we know there are rockfalls on the surface of Mars. It would be neat if that could be corroborated with surface evidence of a rockfall (I think a few have even been captured by satellite!)

Impulsive quakes on Earth have a characteristic waveform which this does not match: The arrival of a compression wave, followed by a larger shear wave. That waveform wouldn't be much different on another planet, since the shape of the waveform arises from the mechanical properties of rock. If it were not a rockfall, it would have to correspond more to a seismic tremor, which happens more slowly-- I know less about those and I am curious how this matches up.

Having multiple stations would really help to narrow down what the source of sounds like this could be.