"A large number of collisions or packet drops have occurred on port"

[Kelvin.uk]

We are experiencing intermittent ping time outs and high ping latencies on some of our servers.

Two out of four of our switches occasionally get "A large number of collisions or packet drops have occurred on port" alert messages which I suspect could be part of the problem.

These two links shows the frequency of the alerts we have been getting:

https://dl.dropboxusercontent.com/u/10321407/switch2.txt

https://dl.dropboxusercontent.com/u/10321407/switch3.txt

I suspect a "rogue device" is connected to our network which is causing this problem, but struggling to pin point it. Can anyone can help us with this?