JBL PB12 Subwoofer "repair constant thumping" Questions

...constant machine gun "thumping" connected to system or not. Serial number begins with "AM0035" and was told these amps cannot be repaired.Is this true? What now? PB-10/12 using bad designed Class D ...

...constant thumping noise. I replaced the fuse, but it makes the same noise. I was wondering if it is blown or if this problem sounds familiar and do you think it's repairable? I figured the sub-woofer ...