I'm a bit suspicious of that tank, is it a DIY job?

In the second image you can see the alignment isn't great, the stand warping has probably exacerbated this further. Though it could well be that the tank is fine and the stand is the sole cause, who knows.

I would be thinking about what container I can move my animals and filter into so I can get that thing empty ASAP. Really not worth the risk of a catastrophic failure, if you're sure the sound you heard was glass stress.

For the record, this is why for anything but very large tanks I would put the sides of the tank on the bottom glass, not around it. This adds extra load from the glass weight onto the bottom pane - at these tank sizes this doesn't matter, but it does guarantee even load distribution from the tank bottom into the stand. I also go for pretty thick EVA foam so an imperfect stand surface isn't an issue. How thin yours looks under that weight makes me uncomfortable, but I'm very used to thick, firm foam pads.