Switch going crazy - question

Ok, here's my network layout. I have a DSL line going to a Cisco 678
DSL modem. That modem feeds a 5 port switch. There are 3 servers
hooked up to that switch, each with a external IP. One of the ports on
the switch goes to the WAN port on a Linksys BEFSX41 firewall router.
The WAN port also has one of the external IP addresses (set up as a
static IP). Other computers, internal network, is hooked up to this
router/firewall.

Here's my situation. The port on the 5 port switch that goes to the
WAN port on the Linksys is going crazy on the 5 port side. But there
doesn't appear to be any traffic I can see going through (from the
Linksys side).

On the internal network, the computers are having really, really slow
internet access........

Does anyone have any suggestions on things should be set up, or things
to look for so I can resolve this issue?

If there are any questions I can answer to help resolve this, please
ask and I'll let you know.....

Thanks!