Hi Louism, and welcome to the SOS Forums!
If it’s just hum then there are specialist notch filters that can deal with it - you
just set the frequency (50Hz or 60Hz) and it will notch out 50, 100, 150, 200 or 60, 120,
If it’s background digital grunge then using a fingerprint filter
should do the trick - find a short section containing just the background noise, click on
the Learn button, then apply this to the offending bits.
Remember also that
with a standard tuned guitar, the bottom E is at 82Hz, so you should be able to roll off
anything lower than that.