...I do have the film still on my screen...
thatīs the reason.
The film that is on the screen if you get the PA4X out of the box the first time is NOT for use !!!
Itīs only to prevent the screen from dust and scratches... And it may cause electro-static discharges that can cause the "sound-switching".
If you use it for a longe time grease from your finger-tips may reduce the "dis-function" a bit.
You should use a protection-film from a tablet and cut it so that it fitīs.
In germany one dealer sells them fitting for the PA4X ( I gave him the dimensions of the screen and he produced them )