There is an invisible wall that appears after you do some damge to Soundwave.

I can't get the exact moment, but here is where it starts. If you use Jazz's (and others, I just used jazz) blaster attack, you can stay still after the screen movement so he dosen't notice you, then push soundwave back until he goes behind the wall.

Ah yes that is a known bug I'm trying to figure out an option for that.