Mine makes an audible 'swishing sound' but it's nothing over the top...You can barely hear it inside the car.

Things I've noticed:

1. 3 x louder after travelling 2-300 km on the highway
2. Noticably louder on hot days (like today)

Sounds like a cavitation issue to me Joe.

What fitting is being used in the pumps outlet?......Has the check valve been removed?

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