hm, too bad your theory (probably) isn't there in total anymore, I like reading pseudoscience, even if it doesn't make too much or no sense at all

Well... After I read the thread title, I couldn't stop myself from thinking... What do we know about Freespace? There is subspace as the ultimate pseudoscience plot device. There is no mission in which the player didn't travel through subspace not too long before the mission - even if we start from a hangar, those destroyers and frigates jump through subspace all the time as well.
So, let's work with that. If we have subspace confirmed and consider it indeed as some sort of shadow or additional 4D-Spacetime sort of "underneath" normal space, then let's just add another mesh between them, which in itself does not have any euclidian geometrical properties, but is more like a network of uncountable but finite quantum particles - compareable with the spin network proposed in loop quantum gravity at least concerning it's consistency.
Because this "plane" - let's call it interspace because that sounds cool - is between space and subspace, it reacts to anything that bends spacetime, so any mass or energy leaves an imprint in it. Anything that moves creates waves like you would expect in a medium like this. Any mass or energy that vibrates, creates a resonation in interspace, mirroring the vibration of the object in "normal" space - just out of phase.
Now, any object that passes into or out of subspace travels through the interspace mesh, and undergoes a process somewhat compareable to ionization. After it returns to subspace or space, it is still entangled in remnants of the interspace mesh, much like someone who walked through a spiderweb. Objects entangled in interspace remnants "recover" after several days. Until then, the vibrations of interspace are again projected onto the objects itself. This means the ship, air and ear of the pilots get to hear stuff - IN SPAAAACE!
Movements of planets of course cause ripples and waves in interspace as well, but their frequency is so gigantic, that it is impossible to even reliably detect them.
Also, because the actual sounds and the interspace waves are out of phase, there is no feedback in your ship for the sounds you make yourself - you actually hear the mechanics of your own ship a lot qieter than they really are - and even your monstrous afterburner and futuristic superweapons don't rupture your eardrums, because the interspace "sound" cancels the actual sound to a certain degree.
Another important fact is, that the interspace "sound" travels faster-than-light. That explains why any two sounds can be heard instantly, even if there are several kilometres between the sources. While traveling through interspace, the "sound" also loses intensity exponentially, much like electromagnetic waves.
Of course there are still several problems with this. If an object moves relative to what? Space? You can't move relative to just "space", that's basically why relativity kicked the aether-theories out of the window. But hey, it's pseudoscience, so now we have some sort of ether again. Suck on that Einstein!
