Bikes4two, it hopefully appears that I *might* of solved. I undid the front wheel nut which carries the power cable to the motor. I made sure that the cable was in the slot in the nut and tightened it up again. I've ridden back from town some 2 miles with a nasty up hill bit at the end and heard no light scraping sound as before. I could have strained the cable causing a poor connection to one phase? It's early days but all available digits are crossed!