Hissing sound from under sink

[Seo195]

Heya,





So there's a hissing sound coming from underneath my sink that feeds my washing machine and dishwasher. I initially thought it was a weeping connection or a pinhole in an old pipe, so I turned the water off. The hissing was still there but as soon as I drained what was left in my cold tap it stopped. My brother who is not a plumber but has been in the building profession for many years also took a look and neither of us could find any leak or any wet spots of any kind. I also checked the back of the washing machine and dishwasher, everything is working as it should and I have since turned my water back on. The hissing is still there however, my brother mentioned something about the water company increasing the pressure during the summer? But I don't know if this is true. I am on a mains supply. He also said it just sounds like water in the pipe, but I'm still not too pleased. Don't really want to bother a plumber when there is no actual visable wet patches though.

Any idea what it could be that is causing the hissing sound, maybe air in the pipe? It's not bothering me but I just don't want a massive leak if pressure is building.





Any help is much appreciated!

 

[Basher]

Have you tried turning off the supplies to the washing machine or dishwasher (maybe one at a time), while leaving the rest on? Just wondered if the solenoid valve in either of those is passing and making a noise, though I would expect that to result in water in the machine at some point!
I suppose it could be conducted noise from somewhere else, like a toilet cistern upstairs or water tank. Are any toilets showing water running a tiny bit into the bowl?

 

[Seo195]

Heya, thanks for the reply. Yeah I turned them off separately and checked them, it was still there. I checked the upstairs plumbing too. I think I have located it behind an old skirting board which is behind the kitchen unit for the dishwasher. I was thinking maybe the pipe was ran and never attached to anything? It's a very old house. Going to take this off for a good look.