asterisk users - Apr 2004 - Severe hum in recording

Hello,

We've made thousands of recording on our Asterisk system, and we had one
last night that ended up having a constant loud hum throughout the entire
recording. None of the other recordings from last night have the hum and the
caller said the conversation had no hum in it. Anyone have any ideas how the
recording could've had such a loud hum when the calling parties didn't
hear
it?

The call was a SIP -> T1 channel call over a T400P Digium quad T1 card.

Thanks,

MATT---