When I hold up my controll stick flicks up and down (only left stick)

Any time I hold up-left, up-right, or just up in general my left stick flicker up and down. I bought a refurbished power a controller that worked perfectly fine the first week but now its acting up. Sometimes my character won't even move since the input says my stick is flicker up and down. This does not happen when I hold down and the problem seems to largely disappear when its connected to a charger.

Hope this helps