It says that there's an image attached, but when I read your post there
was no image. Maybe I'm the only one, or maybe there was an error.
The only thing I think that could be from your description, and having
not seen a screenshot, is that your y axis is set to autoscale, and
you're seeing it bounce around the sawtooth because of its fluctuating
value.
If that's not the case, post another pic, or your vi!