I have a firestore fs-3 along with a shure prologue 4 channel mixer both connected to a canon gl2 camcorder. The camcorder is powered by it's on board battery.

If use the same battery source(separate from the on board camera battery) for both the fs-3 and the shure mixer I have audio noise when the firewire cable is connected between the fs-3 and the camcorder.

If I use a separate battery for the mixer and fs-3 the noise disappears.

If I use the same battery for the mixer and fs-3 and disconnect the firewire cable between the firestore and the camera the noise disappears.

I have tried both an ab pro former battery and a lead acid battery, same results.

Tried a different firewire cable and xl1 camera, same results.

Swapped the fs-3 with the fs-4, same results.

Basically the problem is...
using the same battery for the mixer and firestore there is noise in the audio. If I use one battery for the firestore and one battery for the mixer audio is good.

The audio noise appears to change with the hard drive activity, but the noise is noticeable even when the drive is idle.

For mobility I would like to use just one battery.

Any ideas on the cause of the interference and how to correct are appreciated.

is it some kind of a bastard ground loop problem?? i wonder if the shure unit is grounded to it's own case.

shooting off the hip here, lol, how about a noise filter? similar to what you'd do with engine noise on a car stereo?? caps won't pass direct current, but they will pass the noise to ground because it's a rapidly alternating signal.

i would call up shure... let us know what they recommend.