Hello & Welcome to Just Answer,
Sorry to hear of any issue you may have with your phone(s).
May I ask:
1) The model of the MAIN base unit of this system?
2) The TOTAL number of handsets you have connected to the base? If more than one handset, do ALL handsets have this same issue?
3) What is the AGE of this system and WHEN did this issue first begin (or was noticed)?
OK - can you CONFIRM that these 4 phones are ALL "cordless handsets" that are connected to a single base unit?
And that MAIN BASE UNIT should have a DIFFERENT model number printed on it, such as 4215, 4210, etc.
Also, have you EVER replaced the batteries in ANY of the handsets, and if so, WHEN was the last time that was done?
Hi again and thanks for that information.
OK - can you tell me if this particular handset is ALWAYS used in one particular room or location?
AND, does that room (location) have ANY "electrical" or "electronic" equipment in the area?
NOTE: This equipment can be almost anything from overhead florescent lighting, microwave oven, Wireless router, etc.