Boost Audio / Reduce background noise...

There are a few things that can kind of help, sort of, maybe, sometimes... but the general rule with audio is, unfortunately, GIGO (garbage in, garbage out). Apps like Soundtrack Pro and others have noise reduction filters that let you take a sample of the noise you want to try to remove, but unless that noise is very low level compared to the signal you'll often end up with gross, digital-sounding mess on top of the audio. It's a pick your poison situation really. There's no magic bullet, that's for sure.