Hi and welcome to JustAnswer,
Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, does the problem / symptom persist if the handset is even very close to the base unit?
Any new/additional/replacement electronic devices added lately? ...modem, router, alarm, clock radio, electronic lamp/dimmer or the likes?
Appreciate the additional information; very significant.
Have you tried plugging in the base unit's AC wall adapter to another outlet? ...or moving the base unit even a few feet away from its current position?
Yes please; as these are the only easy user doable tries.
All others would be internal to the base unit.
Please post back results / observations of the above once tried.
Is there another device using the same telephone line? say a modem>
I understand and this is very significant; i.e. if another device connected to the same telephone line/wires does not exhibit the symptom, then it would be an internal hardware issue with the base unit of the Panasonic KX-TG4771.
Is this still under warranty?
Are you considering having it repaired? If yes, it would be to your advantage to consult with and/or seek the services of an authorized Service Center.
Though it has to be pointed that if no longer under warranty, repair fees may not be economically justifiable.
Still, would you like information on locations of authorized Service Centers?