We have a hot water solar panel system in our house and there seems to be a constant humming sound throughout the house. Not everyone notices it but it is definitely there and is causing sleepless nights. We have had plumbers and electricians in to try and determine what is causing the noise and have ruled out mains electricity, the heating and mains water supply but now wonder if it could potentially be related to the hot water solar panels we have on the roof ? The solar system is a closed loop with a hot water tank upstairs and the panels themselves located slightly higher on the garage roof with the connecting pipes running through the loft. I have noticed a small leak in one of the pipes connecting to the hot water tank itself and wonder if this is causing a constant flow through the loop which might be causing the noise or if anyone else had any other ideas of things to check. The noise itself is like a low revving car engine, if this helps at all. Thanks in advance.