harry newton wrote:
I haven't worked on speakers in decades.
http://wetakepic.com/images/2017/12/04/speakers1.jpg

How do we debug a scratchy sound?
We can isolate it with the balance to a single speaker.

But is it the speaker?
Or something else?

You can swap the speaker for the one from the other side. But "scratchy"
sounds are apt to be rubbing voice coils which you can feel by pressing
on the cone with your thumbs.

If it's the speaker, where is a good place (other than the dealer) to get
speakers to fit a car rear deck? Are they all standard sizes nowadays? Or
is each unique?

There are several standard sizes. You can buy cheap replacement speakers
from chain auto parts stores. You can buy the same speakers for half as
much from Parts Express but then pay postage on them.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."