Suzzee,
For the first (and only the first) year that a potable pump is in service, it will not do as you describe. After that, they all do. The 40+yo PAR thumpers used to take two years to start, but after that....
Unless you are real sure of your situation, enjoy it. When you hear it, you know that the pump working and you have water in the tank. On one very rare occasion, the as less than expected. I later found that one of the system drains was dripping - about one drip every three minutes. When I fixed that it when back to one thump every half an hour or so. That is often due to the internal leakage of the pump valves - I have discovered.
Matt
