pio7=0 would work if the io7 was configured for output.
You have io7 configured for PWM, so pio7=1 and pio7=0 are less useful.
I achieve silence by
Other settings tend to have a slight residual noise.
No. There is no means to execute a Nextion side timer across HMI pages.
When you change a page you have emptied the old page out of memory to load in the new page. Therefore the timer is not in memory when you want to run it from another page.