I have used the SCB-68 with accelerometers in the past and did not notice this type of behavior. However, I also used the DAQ card in differential mode instead of single ended. You may want to try that to see if it solves your problem (assuming you are not already doing so). You can still tie one of your inputs to ground, if your sensor needs this.
You have probably already done this, but check to make sure your connectors are clean and the input wires are clamped well. I have been burned by accidentally clamping the wire insulation, pinching through it, and getting a flaky contact.
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