Mower makes awful noise when I take foot off brake

The last time I went to use my mower everything started out fine. I had started riding and cutting with it, no worries. Then, I noticed I big tree branch in my path, so I disengaged the blade and locked in the clutch brake. When I returned, I took off the brake-lock and took my foot off the brake. Next thing I know, I'm hearing this awful grinding noise that only stops when I press down on the brake. Even the slightest touch on the brake will stop the noise.

I was wondering if this means that the clutch belt has been over stretched or if there is some other reason why this is happening.

Thank you for taking the time to review my request,

Help Plz