I'd probably use
Audacity instead, it's an open source audio editor, and apply a noise remover filter of some sort to achieve the result you're after

If it's anything like when I've done this stuff in CoolEdit, you select a "silent" sample in the clip containing the rumble only, to allow the software to get a profile of the noise you don't want, then you can apply that filter to the whole track to remove the background noise. You may need to experiment a few times with stuff like how strong to apply the filter etc. to see what sounds acceptable in the end
