Remove musty smell

Probably the sound dampening material inside at one time or another got wet. You can try, if possible, open the cabinet or remove the woofer to gain access to the inside. And even if there is no sound dampening material, try either spraying Ozium available at Auto parts stores, or fresh coffee grounds. Coffee grounds absorb odors, Ozium eliminates via masking and neutralization.
That is my guess without smelling or seeing the speakers.
Good luck.

If the oder is coming from inside the speaker, open it up, and very carefully spray some brake clean on wherever the oder is coming from. It dries almost instantaneously. Just don't get any on the exterior of the cabinet or drivers. It probably won't hurt the finish, but I wouldn't tale a chance. And only use brake clean. Smell it before you put any on the speaker. If it smells like calibrator cleaner, pick a different brand. Good cleaner doesn't have a strong oder.

Or baking soda.

Or, replace the malodorous damping material with new Acousta-stuff from Parts Express, or another of your favorite batting. Also, remove any mice while you are in there :~)

You guys have some good ideas! I thank you all.

An ionizer is the only thing I've found over the years that completely eliminates odors.