Philips Pronto TS1000 - Manual (Page 24)

This tip does not apply to the Philips ProntoPro:
The very faint buzzing sound is made by the inverter, part of the circuitry that generates the higher
voltage needed for the display's EL backlight from the low voltage provided by the internal battery.
This is completely normal, there is nothing to worry about. You need to be in a very quiet environment
to hear it. All similar backlights used in other devices such as watches and palmtops make the same
sound.
A6−10 What else can I do to troubleshoot random problems?
In addition to the tips mentioned above, if you're running older firmware you should ensure that IR
code labels do not contain spaces. These are not the actual button labels, but rather the internal code
label that reads, normally, "LEARNED". So, instead of "TV − Power On" you could use
"TV−PowerOn".
Other suggested troubleshooting tips include replacing the batteries, re−flashing the firmware,
uploading and downloading your CCF file again, and ensuring that you are running the most recent
firmware revision.
Worse comes to worse, sometimes gently shaking or tapping the remote can help things.
RC: Philips Pronto & Marantz RC5000 Unofficial FAQ 24