radio buzzing...

["G. Benedikt Rochow" <rochow@segosf.hlo.dec.com>]

While I sort-of play a EE at work, I'm not real familiar with
noise suppression: The simple old Sony cass. deck that came with
my 84 5kS buzzes rather a bit, in sync with RPMs I believe. 
While temporarily fixing loose wires in the really sloppy
installation (twisted-together wire ends with a bit of electrical
tape over them), I noticed that the blob of whatever-that-is
that's usually around the 12V (?) wires isn't there.

What do I need to replace there, some sort of ferrite ring?
Around which cables does this go? (I dimly remember things like
+, + and ground, and also all-the-data-and-power-wires-there-are
on an old Sinclair printer...)

thanks for any advice (the buzzing rather interferes with "Autobahn",
don't you know).

-gbr