I'm having trouble with my Ryobi OLT1832 line trimmer. I've searched the internet but haven't found anyone describing precisely the same issue. I pull the line out to the length required to just touch the guard. When I start up, any little excess gets clipped off. But within 10 seconds or so, the length of the remaining line within the guard has been shredded to only about 8cm long, rendering it useless as a trimmer. I've replaced the line (with the recommended spool) and it made no difference. Any thoughts on what might be causing this problem?