This is more of a general physics question to help me understand how to choose sports headsets in the future, however it is too specific to a certain use case (bluetooth headset) to belong in the Physics StackExchange.

Problem:

3 of my 4 sports bluetooth headsets suffer from choppy sound quality (signal interference?) the minute I step outside. It seems to be especially bad under a clear sky no matter the time of day.

The 4th and the most expensive headset does not suffer from this, but it has a different (more compact) design. The worst performance was by the cheapest sports headset (from ebay) and it was unusable outdoors.

Observations:

• In all cases my phone is located in my trouser pocket, but moving it closer to my head (the headset) seems to lessen signal interference, but not remedy the issue completely.
• In all tests the headsets have been fully charged.
• The speed of movement also seems to play a factor, but I am not able to reproduce that affect every time.
• I can say that clothes are not a factor, as the same clothing indoors produces no interference.

Theories:

• background EM radiation coming from outer space?
• EM radiation coming from our sun? Although I have not observed if the moon reflecting the EM from the Sun plays a part or not.