Intermittent slow response from Squid

[Moses Truong <moses_truong@xxxxxxxxxx>]

We have squid running on a server with delay pools enabled. The 
squidclient usually responds very quickly - in less than 0.03 seconds 
most of the time. However, there are times when this rises to over 39 
seconds.

There are 2 Gb of RAM, and there's about 900mb used.
There's 1024 file descriptors, and the largest opened hovers around 370.

Could anyone suggest what I should be looking for to track down why 
squid sometimes take so long to respond? Thanks.