Well, the noise is gone as are most of the other problems. It was the conditioning that was not sufficient.
Here are the correct conditions for 12 guage Silver wire. They are stronger for the 1 oz billet.
4 minutes treatment in 1 M NaBr with 3.5 V from two AA batteries. The Silver electrode you are going to use is connected to the positive (red) pole of the batteries and the negative pole (black) goes to the donor electrode which is also Silver of the same purity. The Silver electrode will blacken significantly during this 4 minute conditioning / plating. The electrode must be then washed with distilled water and must be stored under distilled water. It will last for at least 24 hours. After that, the readings begin to become unstable again.
From the start of the conditioning, the operation and storage must be under reduced light as you are creating a light sensitive surface on the Silver electrode.
Insure that all sides of the electrode are plated evenly and slowly over 4 minutes. If you plate more than about 12cm of #12 wire, you may have to use longer times or higher voltages. I find that a 20 gram billet requires 9V over about 3 - 4 minutes.
If your readings are low, you have overdone the conditioning, and if they are high, you have underdone the plating. You must have an even coating on the Silver electrode which does not flake off during use. This was one of my problems.
My results in two tries? 1: -115.5 and 2: -116.1, Calculated is -116.96. These were at 20 deg C using 1.0 M NaBr with stirring.
Cleanliness and proper storage along with the right conditioning seems to have fixed up all problems. My thanks to Kirk Keyes for 6 inches of 99.99 fine #12 Silver wire.