Were the beeps more like low-pitched sounding dongs?
If so, it could have been the toilet smoke detector being activated. If it were the higher pitched dong, it could have been the seat belt being cycled on-off-on which would generate 3 dongs.
BUT if it was the toilet smoke detector, unless you saw the cabin crew running around with fire extinguishers and wearing smoke hoods and fire gloves it would have been a false alarm (for example hair spray can set off Airbus toilet smoke detectors)
If the cabin service resumed straight after the crew member had spoken to the flight crew then there would have been nothing to worry about
