On a journey today, after covering around 150 miles, I stopped at traffic lights and heard a loud humming noise. I looked around at the cars around me to see if I could identify who was making the noise. When I pulled away the noise followed me and I suddenly realised my super silent 'Tessie' who has hardly made a murmur in the past 15,000 miles was the culprit. The humming sound has now continued for the next 300 miles. it is of varying intensity, sometimes hardly audible but sometimes very loud. The pitch and amplitude is not consistent but 'breaks up' almost like an old AM radio signal fading in and out. Do you think that this might be the battery pack coolant pump? Has anyone experienced this kind of thing before?