Strange Scary Sound In The Sky!

Was out walking my dog earlier today and started hearing these horrible noises coming from the sky. I still have NO idea what they were but can assure you that it wasn't coming from the pylons behind me. I walk here nearly every day, and never before have I heard anything like this! I and the other dog walkers I passed were all pretty sketched out!! Went on for about 30 minutes before it stopped.
Does anyone know what this was? I live in Dorset in the UK, near Bournemouth.