hissing is miss
unfortunately, hissing will rarely if ever be fixed by a software update. it is a hardware 'flaw' where the amp of other elements are efected by other hardware. usually it comes from dirty circuitry or overpowered components that do not have proper reigns.
i think that maybe this may be due to too many items inside the touch. it has wifi, touch and movie/audio items inside. if it were a simpler machine, these problems would not occur. unfortunately, a simple fw update will not fix this, but rather hardware redo