I'm very new to home audio, so please forgive any ignorance. I have a powered sub hooked up by a single RCA cable to my receiver (as instructed by the user manual) and the filter knob to LFE. It has worked without a problem for a couple years, at least I haven't noticed an issue. Now, when I began playing a record on my turntable, which is connected to my receiver via a phono pre-amp. I've checked all connections and it all seems snug. I don't have a space RCA cable to try replacing my existing one with, so that's still an option. The crackling doesn't seem to get louder or lower when I adjust the volume. I tried to switch to a different input on my receiver (my Xbox over hdmi) and the same issue is present, but when you're not right next to the sub, it's difficult to hear the problem. Can anyone help with some troubleshooting?