castlegarden ride on stopping ?

my castlegarden twin cut 15.5 hp mower stops with a high pitch noise when it happens. It dosent matter whether or not the blades are engaged. The noise is high pitch and continous and when you try to start again it will do so but will cut out again with the same result. This will happen several times and eventually it will run fine . The next time you try to cut the problem will start all over again