Broker keeps rebalancing

Hi there,
My kafka client is reading a 3 partition topic from kafka with 3 threads
distributed on different machines. I am seeing frequent owner changes on
the topics when running:
bin/kafka-run-class.sh kafka.tools.ConsumerOffsetChecker --group
my_test_group --topic mytopic -zkconnect localhost:2181

The owner kept changing once a while, but I didn't see any exceptions
thrown from the consumer side. When checking broker log, its full of
INFO Closing socket connection to /IP. (kafka.network.Processor)

Is this expected behavior? If so, how can I tell when the leader is
imbalanced, and rebalance is triggered?
Thanks,
Chen