So in a Wikipedia article about space debris I read that:
At higher altitudes, where air drag is less significant, orbital decay takes longer. Slight atmospheric drag, lunar perturbations, Earth's gravity perturbations, solar wind and solar radiation pressure can gradually bring debris down to lower altitudes (where it decays), but at very high altitudes this may take millennia.
Since debris decays at lower altitudes (presumably LEO) there has to be a mildly dense medium of matter/gas in that altitude. So if there is a medium then energy can flow through it since it is not really vacuum.
Can pressure waves (like sound waves) flow in LEO?