@Paul_Violin:  Is this a new instrument you just got, or is this a violin that was playing fine and has developed this odd/unpleasant sound?

Not being able to actually hear the problem or look at the instrument, my first guess with a "crackly static noise" would be that something is vibrating against something it shouldn't be, or that something is not making as good contact as it should be. 

It could also be something is coming apart, like the top plate coming apart from the ribs (sides), for example.

I would guess at mechanical vibration of one of those sorts, since you mention the problem is noticeable when playing on the lower strings, which usually vibrate the instrument a bit more.

Look for easy things first.  You already noticed the soundpost maybe doesn't look quite straight.  That might be it, but I would look for easier things before trying messing with that.

Is the chinrest perhaps touching the tailpiece at any spot?  It shouldn't be.  That can make some very odd noises.  

Are both the feet of the bridge exactly flat on the top of the violin as they should be?  If they aren't, that can cause some weird sounds.  If you can get even a thin sheet of paper under any part of the feet, they aren't fitted right, or the bridge is perhaps leaning.

If you use fine tuners, are any of them loose?

If you use a rigid type shoulder rest, is there any way it could be touching the back of the instrument when you have it up in playing position?  Try taking it off and see if the sound continues.  They can look fine when you are holding the instrument and looking at it, but can touch the back when actually up on your shoulder with your jaw down on the chinrest.

If you can get it to make the noise when just plucking the G or D strings loudly, then you can try plucking those strings while touching the different parts of the violin (chinrest, parts of the top, tailpiece, etc).  That can help in figuring out what is vibrating/rattling.

Since you clean the violin every time you play it, you probably would have noticed if the plates are coming loose from the sides, but you might want to check that anyway, looking very close.

You can also try holding the strings down in the nut slot by pressing each one down, one at a time, while bowing the open G and D string, using a fingernail.  If that stops the sound you're hearing, then the nut slot might be too wide or badly shaped.

@augustoad: So far as the "VSO" matter... any of the possible problems I have listed can also happen on "proper violins".  I don't like painted fingerboards either, but they aren't really very likely to cause the sort of sound problem described.  Neither are cheaper grades of wood or thicker ungraduated plates, which are typical with less expensive violins.  Even compressed wood is more likely to just not give much volume or not have a very pleasant tone than only sound bad on the G and D strings.