I have caterpillar reach truck, model# nrdr30 ser.2gl. After 5 to 10 minutes, with key on. The truck carriage would begin to raise and horn would sound off. Found no error codes on display. Checked hand controls, micro switches, contactor, and connections....Found no issue's. Powered unit back up. Now, unit is in normal operation. Would like know what would cause this issue? Ghost problem. Appreciate the help!