Hum on a subwoofer amp is highly (but not 100%) likely caused by a bad capacitor. If the amp is "infamous" for this problem then there is a good chance there is a specific capacitor that commonly goes bad. I've fixed this sort of issue on different brand subwoofers. If you know someone who repairs electronics or have a shop nearby that you can trust then it's probably worth repairing. They are usually not too difficult to solder as it's usually a through-hole component going bad and not a tiny surface-mount component (though that can also happen especially with multi-layer ceramic caps (MLCC) which can crack as the ceramic is brittle). But these cases are usually bad electrolytic (or sometimes tantalum for older equipment and those are basically a specialized type of electrolytic anyway) and often have leaked fluid and/or bulged tops to make it fairly obvious where the bad cap(s) is/are.
Are the sub and box still in good shape? Are you still happy with it other than this amp issue? If you cannot or do not want to repair the amp, you could also do a block-off plate and get a rack amp. Dayton (Parts Express) has rack mount ones, or Class D (ideal), G or H pro amps can be a good choice.
Last edited by DonoMan; 06-22-2018 at 08:30 AM.