When I did a teardown of my JBL Spyro sub, I was pleasantly surprised with the overall build quality with one exception — the speaker cone surround.
Of all the available materials for the diaphragm surround, they chose to go with a flimsy foam that tears more easily than wet 1-ply bathroom tissue. This was the cause of my humming.
To fix the tear, I used E6000® Permanent Flexible Adhesive and a patch. I used a BAND-AID® Brand Flexible Fabric Adhesive Bandage because it was easy to apply and is engineered for flexibility. Use just enough E6000 to cover the BAND-AID*. I let the adhesive cure for at least 24 hours before testing. The results were excellent.
*Do NOT overdo it with the glue. I added extra adhesive to see if I could make it more resilient to kick-bass at maximum volume. It made the cone too heavy and stiff so it doesn’t sound as good anymore.