Help with "popping" Quad 2805

I purchased a pair of Quad 2805s here on the forum.  They arrived last Tuesday and after unpacking and plugged them in one of the speakers immediately starting making a popping sound.

The seller has been unresponsive and I need some sort of repair before I can use them.  I'm in a small town and would have to ship them to whoever can do the repair.  Will probably have to wait a couple of months as I spent way over my budget on these.

Any help provided is greatly appreciated.

Thanks in advance,

Bob