Since you say the problem is in only in one speaker, I would first swap the speaker cable connection R->L, L->R, and see if the problem moves to the other speaker.
This will tell you a couple of things. First, it will confirm if the problem is just in the one suspected speaker. If you don't get the buzz with the cables swapped, you know the issue is/was in that suspected speaker. If the buzz does move to the other speaker, then the problem could be an issue with the design of that particular speaker model, or it could possibly be something in the chain before the signal reaches the speaker.
After the experiment, don't forget to swap the cables back to the original position and reconfirm that you still have the issue before you start "digging into" the speaker.
Anyway, it's free and it's easy to make the swap to insure the issue is really in that one speaker.
Enjoy,
TIC
This will tell you a couple of things. First, it will confirm if the problem is just in the one suspected speaker. If you don't get the buzz with the cables swapped, you know the issue is/was in that suspected speaker. If the buzz does move to the other speaker, then the problem could be an issue with the design of that particular speaker model, or it could possibly be something in the chain before the signal reaches the speaker.
After the experiment, don't forget to swap the cables back to the original position and reconfirm that you still have the issue before you start "digging into" the speaker.
Anyway, it's free and it's easy to make the swap to insure the issue is really in that one speaker.
Enjoy,
TIC