Why doesn't my starter sound right?

So I bought a 2.0kw genuine Mazda starter for the first couple of weeks it sounded great it was spinning quickly and the car started up both cold and hot.



Now the starter feels like its spinning so slow doesn't make the same winding noise as it used too, the compression is good on the car but because the starters barely spinning it won't start when hot so could it be a battery issue or connections?/ground?



thanks