Speaker rubbing is usually do to the voice coil rubbing against the magnet.
It can be caused by playing the speaker with an amp that is more power than the speaker can handle. Your combo doesn't seem to be too much power but power ratings on speakers and amps aren't standardized so it's easy to mismatch speakers with amps.
In a car stereo it can also be caused by mechanical damage due to rough pavement and potholes. More likely to happen in a pickup than a caddy.
Woofers can be rebuilt rather than be replaced. If you are interested in that option check with Bill at millersound.com
They are the best at speaker repair.