[grog11]

Try this before replacing the pump.

There is a vacuum down procedure using a hand vacuum pump applied to a special reservoir cap with the engine running a few minutes to purge air bubbles. Air bubbles get stuck in the system, causing the growling, the vacuum draws them to the top.

In a pinch, without a vacuum pump, you can actualy use a shop vacuum. Apply the tube to the opened reservoir cap, with a duct tape seal, or even wrapping a rag around it, running the engine a few minutes while vacuuming.

If the vacuum does not stop the growl, you probably looking at replacing the pump.