Noise from my series bass when using batteries

[jazzyvee]

Today I had a practice session using my series I short scale bass through my new Stanley Clarke Acoustic preamp. I used headphones and my pod and my bass using the stereo to mono cable.
When doing this I get constant hum noise which is similar to the noise you can get if the jack is pulled from the bass when the other end is still connected to the amp.

I checked the cable and all the connections are fine, the two resistors in the stereo jack end are connected and I get both pickups through the preamp.
The sound is not directional and when I used the 5 pin cable there is no noise whatsoever from the bass.
Any suggestions on what is the cause.
I normally always use the 5 pin cable which is why I hadn't noticed it before.

[JimmyJ]

The usual troubleshooting ideas: "Electret power" switch should be OFF.  Try all 3 inputs, A, B and A+B.  Try using a known good mono guitar cable and see if you get clean bass pickup only.  Be sure your stereo to mono cable is not wrong way around (I know, obvious, but the results could be odd).

Jimmy J

[jazzyvee]

Thanks Jimmy, i will check your suggestions.  I am working through a setlist for an upcoming gig so will get off the sofa and plug into my rig to see if there is any difference in the noise. BTW, im loving the sound of that acoustic preamp.