Pioneer VSX-604S Left Channel Crackling
So my friend recently gave me some new speakers, and I discovered that my dad had an old Pioneer VSX-604S AVS Receiver. It has A/B channels for front speakers, so I took the new speakers from my friend and put those on A, and my dad's older speakers on B. It works fine, except the left channels in both A and B crackle. I have tested with every speaker on every output with different cables, so I know for sure it is not an issue with a specific speaker or cable. Is there some way to remedy the crackling or am I stuck with it unless I get a new receiver?