Issues with one car speaker giving off feedback? How do I fix it?

[Diablo]

I installed a new amp with inline filters. It was properly grounded. However one rear door speaker continues to make a horrid feedback sound despite tuning the amp and replacing the physical speaker. How can I fix this or what can I do?

 

[Karle]

shield the wires.....sounds like there is a power wire some were close enough to cause feed back.......try opening that door if feed back goes away then u no its the wires run down that side of the car in the door seal....if it doesn't its probably in the door...