weird noise coming from path next to drains

hi

just noticed today that there is a strange repetitive noise coming from underneath (as it seems) my backgarden path. this path is next to the drains,i am worried that the could be blocking as the water level in the toilets seem low.

any help would be greatly appreciated

ART6

Could possibly be a build up of congealed fat or something at a joint. Sometimes that can cause throttling in the pipe so that the speed of waste water through that point increases, creating a slight suction upstream of the blockage and pulling some water out of the U bend of your toilet bowls. I'd try putting some caustic soda down a sink and running a tap slowly. However, if you haven't used cautic soda before, be very careful. It can get hot when water is added to it, so make sure its poured into the sink trap, and wear rubber gloves and keep your head well clear. If it gets on your skin it can cause severe burns.

Also, check the main drain vent pipe that rises to the roof of the house. If it's blocked that could cause a suction in the drain.

thanks will try that 2moro and let you know if it works