Factory resetting didn't help.
What would I be looking for in terms of oscillation in the filter stages? Are we just talking about either a short between the input and output of one of the op-amps/a faulty IC? Or would I have to look at other components, such as resistors and capacitors in the area?
Getting my hands on an oscilloscope is pretty much off the cards atm; I just can't afford it, and I don't know anyone that has one I could borrow/use.
