Anders,
One of the benefits of all the electric cars now on the market is, it's created a demand for quiet electric vacuum pumps that are specifically designed to generate vacuum for power brakes.
This is the one I'm using:
http://www.metricmind.com/products/706e2/
... but I understand Hella makes a good one too:
http://www.summitracing.com/parts/HLA-009428087/
I'm sure there are others but these are two that I know of. Problem solved!
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