I have this same machine, believe it had this ping thing once or twice - I have found a small piece of thread lodged in the bobbin area. if you figure out what the issue is please let us know. My machine also sometimes mysteriously cuts the thread when I don't want it cut! I turned the foot pedal around so as not to accidentally rock back on it, but ?? it still happens, fortunately not too often.
I doubt this is your problem, but if I have a bobbin that hasn't wound evenly, my machine doesn't like it.
Good luck!