Thanks for all the answers everyone.

I'll give the ferrite cores a go and see if that helps. I also thought about
contacting the ARRL, but since it's a Part 15 device that I'm having trouble
with I figured they wouldn't have much to offer.

Here's some more detail on what we're seeing, maybe it will help:

From the users' perspective, the wireless is very very slow. On our wired
network files copy between computers at between 10 and 20MB per second; on the
wireless getting 500k/sec is pretty good. They also experience high latency
(ping times over 3 seconds (not ms) have been seen) with occasional high packet
loss (as high as 75%).

On the access point side, the controller reports that the individual access
points are properly spaced out channel-wise, but report high "PHY errors" which
our support person tells me means the channel was busy when the access point
went to transmit. They report these errors even with no clients connected.

Our support people tell me that "we're in a noisy environment" and offer no
further suggestions to track down the source. When we installed this system two
years ago we didn't have this problem, so something must have changed.

Thanks again for anything you can offer.

~Ryan W7BEC