They always do this without the prop, the alarm means the magnetic field of the prop is not rotating properly so if it is missing, it definitely sounds the alarm. It will also do this if it is run dry. With 11V it spins or you just have no alarm? If it spins I really think it must be the drive unit (prop assembly) something must be stuck or jammed. Go through the manual or the thread at the top of the forum on cleaning. If you had a wrong power supply the connection would be different so you wouldn't be able to plug it in.