I have the string trimmer attachment and the first couple times I used it, it worked great. But ever since I had to reload more string, it doesn't work right. I know I loaded the string correctly because I read the manual and watched videos. The problem is the string never stops coming out now. I have the strings at a decent length, not hitting the guard when it spins, I pull on them to make sure its locked, and within 10 seconds of use the string comes out and hits into the guard. I cannot get it to stop?