Troubleshooting: faint scratching in speaker (volume down)

All,

I'm sure the possibilities are endless, but anyone ever experience a faint scratching coming from a speaker when the signal volume is all the way down? No scratching heard when the speaker cone is flexed by hand. And no other issues - speaker plays very well to moderate/high volumes. Seems to go away when the system is powered off and back on.

Based on this, I'm assuming it's not a problem with the driver itself.

I'm guessing something else anywhere in the signal chain... amp, EQ, head unit...

Thanks.