I've got a Creative PC speaker, woofer and 5 tweeters. With inputs
disconnected I get a sort of intermittent whooshing or wind like sound.
The volume of the sound is not controlled by the unit's volume control.

Since this is coming from all the speakers, I assume - correctly? - that
the built in power supply is acting up. I assume the built in power
supply is some sort of switcher - would bad caps cause this noise?

Where else should I look. Thanks in advance