The Humming Machine by Berlie Doherty
Young Corgi Books ISBN 9780552554022
When his great-grandpa gets a wonderful humming machine, itís the start of a new adventure for Tam. The King of Faery has seen Great-grandpa and the machine and wants them both, so he magics them off to Faery. Now itís up to Tam, once more, to travel to that magical land and, with the help of his old friends, try to bring Great-grandpa home.