I've tracked down the source of the rattling at low frequencies. The "wing" which is screwed onto the back of the speaker is loose at one post. This wing is covered by a foam rubber piece which covers a thin plastic "diaphragm", which covers what looks to be a port. The "wing" is somewhat horn shaped and one corner is loose but I can't figure out how to tighten it. From inside the speaker it just looks like a wood s***w, however from the outside, all I see is a hole with possibly a very thin copper wire?
Tags: cs300, Polk, Rattling, speaker