Having a wide range of experience like I have, you often find yourself back in a land once long forgotten -- today was one of those days.  I returned to very low level network land to which I haven't been in over 8 years.  We've been having a problem with a port on a switch recently, freaking out and disabling itself.  Not just any switch, a cisco 3600 series.  I hold cisco's in high regard, and layer 3 switches are pretty high on the uber w00t-tastic scale, so just seeing this error was a new experience all in and of itself.  I present the faulty port.

Faulty eh?  Take a look at the port stats and sure enough, there's a BOAT LOAD of errors, more than I've ever seen.  A "rule" is 1% is considered excessive, and we are hitting 1.2% solidly.  Checking out the receive detail, getting a lot of FCS (meaning CRC didn't check out) along with Undersize errors (packets are not the right size) -- so what does this mean?  Nothing specific, it's just info, and in this case, it is incomplete.  Off I went onto the switch, into the telnet console and wanted to know what IT was saying about this.  Sometimes the graphical interfaces don't tell the whole story ...this is one of those times.  I had to really dig into the archives to remember how to get into a cisco the way I wanted (logged in, config mode) so I ran show interface gi0/3 (show me interface gigabit bank 0 port 3) and I get some hotness ...

Again, reconfirms CRC errors but notice no frame errors.  This is a big huge hint - it means the size of the packet is OK but the packet itself isn't checking out.  This leads me to believe its a cable that's run too long or unshielded.  Cables are susceptible to EM, electromagnetic interference and every wire is an antenna, period, I don't care how long, if its got ferris metal in it, it's an antenna.  I put money on unshielded.