External Speaker Static: Problem with audio jack?

A flush connection on your mini-jack will reduce the chance of static happening. Anything less than a flush connection will be like a magnet for static charge accumulating on your gear.

Clean the mini-jack with a slightly moist towelette, the let dry entirely; this should reduce the static sound. Any cleaning solution should work fine.

Do you get the same "static" sound with only headphones plugged in?

Headphones don't induce grounding problems like external speakers. I am guessing the external speakers were all amplified speakers, with built-in amps and some sort of mains power supply. Perhaps you also have some peripherals such as a display connected to the Macbook Pro.

Try this: disconnect all peripherals from the MBP (including the Magsafe power plug) except the external speakers and see if you get static. I will also guess that the static is more of a whine/buzz that changes whenever the computer does something different.

If this works, then you have a common ground problem. The cheapest way to solve this is a Radio Shack ground loop isolator on the speaker cable,

http://www.radioshack.com/product/index.jsp?productId=2062214

High fidelity versions are also available, more like $300USD.

Very good. I've seen it on PCs, especially with external displays, powerpack, and speakers.

If by chance it doesn't work, it's only $18, but it's always worked for me.

Hmm, seemingly a different but related cause. It would be interesting to see if the Radio Shack isolator would have cured the problem with the original USB configuration, or if other devices into the USB hub also cause noise.