Noise transmission through base pipe and rainwater downpipe

Dear forum,

I have the following problem with my small lifting system or my house drainage. If I have chosen the wrong forum, feel free to move my post accordingly.

The small lifting system is located in the basement of my single-family house (built in 2019). When the small lifting system pumps out, I can hear the resulting gurgling noises in the bedroom in the attic. The sound transmission does not occur inside the house but through the base pipes and the rainwater downpipe outside. The noises are loud and bother me. Therefore, I would like to know what I can do about it.

Here is a sketch of the house drainage:



A sewer cleaning company has already conducted a camera inspection of the affected pipes and lines, but no irregularities (e.g., too steep slope) were found. My general contractor said that he had never encountered such a case. Although he confirms that the noises are not normal at this volume, he does not know what to do to solve the problem.

My questions:
- An acquaintance of mine said that rainwater and wastewater are only allowed to be combined in the inspection shaft. Is this statement correct? Could this be the cause? As can be seen from the attached sketch, in my case rainwater and wastewater are already combined in the base pipe.
- What other causes for the noise development could there be? What could be done about it?

Thanks in advance for any helpful advice.

Best regards
Timmy

- An acquaintance of mine said that rainwater and wastewater are only allowed to be combined in the inspection chamber. Is this statement correct?

I can't say anything about the regulations, but it would have been better to have separate piping up to the chamber. Nowadays, separate sewer systems are often installed or switched to separate sewer systems during renovations. In that case, they would have to dig up to your house and reinstall everything. It’s more of a future scenario, but your excavation contractor saved themselves pipes and work for maybe 300€ here (since the pit is open anyway) and potentially caused a huge effort in the future. My tip is that the rain gutter is not decoupled from the house. The gurgling is then transmitted as structure-borne noise.

I cannot say anything about the regulations, but a separate pipeline routing up to the shaft would have been better.

Thank you for your quick feedback. Would a separate pipeline routing have been better only in terms of noise development, or what other advantages would it have? In the area where I live, there is a combined sewer system, i.e., rainwater and wastewater are combined in the sewer anyway.

The main pipe and the wastewater pipe are probably made of PVC. No structure-borne sound will be transmitted through that. If anything, it is airborne sound through the open downpipe leading to the [Regenrinne].

But isn't it already stated in the initial post that the sound transmission takes place through the base pipe and the rainwater pipe?

Could the problem not be solved by a simple backwater valve that dampens the airborne sound?

Couldn’t the problem be solved by a simple backwater valve that dampens airborne noise?

Thanks, good point. If the transmission actually occurs via airborne noise, it could work.