Hi Jacob,
I too have an SA-WX700. The previous owner was aware of a rattling sound coming from the bottom of the unit, but attributed it to a loose part. When I got it home I took it apart and found that the lower woofer is catching on something internally as it moves. The previous owner claimed that he had never played it loud, and I have reason to believe that he was telling the truth (but someone else may have done the job).
Anyway, Sony wants to charge $144 for a new woofer. Of course this is ridiculous as I could buy a new unit for that price these days.
If you are ready to junk your unit, I would be interested in buying one or both woofers if the total cost is reasonable. I am located in Oregon.
What have you heard about the amp other than that it has failed for a number of people?
Matt