I recently sold-off my Troy-built gas mower to a neighbor after committing to using my Greenworks Model 25302 electric push mower. I'm 9 months into ownership with hardly a concern until recently. As I was cutting my (roughly 5K feet of lawn) I began to notice a much louder sound emanating from the right-most motor. I then noticed the battery life for both batteries began to decline rapidly. I turned the mower on its side to inspect that nothing had worked it's way up into the motor(s) housing and was satisfied not finding anything. I inserted my second set of batteries (fully charged) and continued mowing but still hearing the same loud sound from the right motor. Any suggestions as to the possible cause?