Buzzing pipework

[tuppence]

I'm installing a water softener and have modified the rising main but haven't yet connected the softener. Unfortunately the modified pipes now hum/buzz.

The new pipework consists of a double check valve followed by a washing machine tee (softener inlet) followed by a full bore lever operated ball valve followed by another washing machine tee (softener outlet). Is it likely to be the double check valve? Are they noisy sometimes and if so can anything be done about it? I've never used one before.

 

[bengasman]

Hopefully it is not an electrical buzz

 

[ajstoneservices]

Faulty CV's can sound like a maddened bee. Does it happen only when water taps are open.

 

[tuppence]

Does it happen only when water taps are open.

The noise is there even if no water is being drawn at a tap etc. but the loft tank takes forever to stop filling. But if I close the bypass valve to block all flow to the tank, the noise stops.