"ghost" sostenuto pedal sound for keys

I have a Technics pcm digital piano pc 200 and noticed last week that when I play on the keys they automatically sustain the sound like the sostenuto pedal is down (which is not nor was at any point while I played). I've tried unplugging/replugging it in, turning it on/off again, etc. I noticed that if I press on the sostenuto pedal and harshly take my foot off, the sustaining sounds diminish but do not disappear completely. It makes me think that the wiring somewhere might be pinched or something and probably need to be fixed/adjusted.

Can anyone please tell me how to stop this "ghost" pedal-like sustaining sound for the keys even though I'm not pressing the sustaining pedal down? Thanks