Thank you for playing! The game actually has a sound menu in the preferences so you can tweak the levels, but I probably should have changed the defaults before shipping.
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OK, I've checked this out. It looks like that's what Android does while it's preparing the package to be processed by the installer, so it should be a case of waiting it out? On my device (a oneplus 3, so quite high-end) that screen appears for 5 seconds or so, before moving on to the install prompt proper.