2d sprite shifts in place while animation plays

I'll see if I can explain this: Unity Version 2017 4.16 personal. 2D Project. I have made a 34 frame animation of a character performing an action while standing in one place. His feet are planted and do not move as part of the animation. The total size of the sprite grows frame to frame because he is swinging a weapon from the ground to the sky.

The sprites on the sprite sheet are aligned so that his foot sits in the same spot in each frame.

I manually sliced them in the sprite editor so each frame is the same size, and not hugging the character sprite (because I found that if I use automatic, each frame is a different size, and causes the characters foot position to shift wildly with each frame.)

However, even with each frame being the same size, the characters foot oscillates on the spot, making him look like he's vibrating, very noticeably.

I've rechecked the sprite sheet, everything is aligned, if any frames are off, it's only by a pixel or less.

Should the character sprite be moving around wildly while the animation plays, after using auto-slice? I'm not sure what to do as I spent hours checking the alignment of each foot on the sprite sheet.

Thanks