Fitted forge dump valve i can see pistons going in and out but does not make any noise when changing gear?
Answers:
Is it recirculating or atmospheric?
Try fitting a cone air filter, I have a OEM recirculating dump valve on my Saab turbo, it was quiet before I removed the airbox and fitted a K&N open air cone filter, now it makes lots of hissing noises.
More importantly doe your dump valve operate correctly, hold boost at high enough psi etc.
What car are you fitting it to?
A dump valve is just an ornament unless your car has a turbo. Turbo Diesels don't count!
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