speakers or HU, or both?

[vitaminC]

Recently it appears that the speakers in my '03S have died. A while back there was no sound at all from the radio, and now I get sound but it's got a lovely crackle to it. It is not affected by source or balance, and is present at all volume levels. So I presume the speakers are shot and maybe the HU, too?

Don't really want to replace/upgrade the stereo, as I've spent enough recently on other maint issues.

I love driving this car, but the semi-weekly issues are really getting annoying!