HELP!!!! dewalt problem

[NC Scroller]

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[spraypaintcreations]

Hello

I started to use my Dewalt type1 saw today and it has a knocking noise this only happens when the tension it set and stops some time when cutting also if I push down on the are it will quit. It sounds like something is hitting in side of the arm. Doe anyone have a idea of what is causing this?

Thank you in advance
Tom