My magnifi one's subwoofer just makes random popping and crackling noises.

My subwoofer seems to be bad. It just makes popping and crackling noises, but since there is no way to put any input into the speaker, I don't know if its the subwoofer or something with the crossover or wireless connection.
I"ve had the unit connected for about a year, but it sat unopened for a year before setting up waiting for house remodel to be completed.

Hoe can I troubleshoot the system? Is just the subwoofer available for purchase?