The toilet and the sink both drain into the grey water waste lines. Because they are connected by piping, sound can travel through the pipes from the toilet to the sink.
PVC was used instead of cast iron or the pipe is against the back of the wall so the sound is transferred through the wall.
Poor venting
It was horrific. She and her family could only flush the toilet at night, she could hardly make a noise.
No.... because that's just the sound of the water going down the hole and new water coming in its just how a toilet works
I reckon there is no air vent pipe on the drain line of the toilet you are flushing and the siphon action is sucking out the water in the loft toilet also.
the reason why the toilet makes noise when you turn water on is because all the water lines are conected so when you turn on water the toilet gets affected and the water that goes down a drain goes to the water pipe.
Sink is not vented properly and the water from the p-trap under the sink COULD be sucked out by the hydrostatic pressure from the toilet flushing.
Usually the water filling up the flush valve in the tank. If it's bugging you, you can change the flush valve to a new one.
Your ballcock is comming on -- replace tank ball or sometimes you have to change out flush valve -- but change tank ball first and see if that will do it You hardly ever have to change flush valve -- Your ballcock is what lets water come into your tank
If the toilet and shower are in an upper floor then there is a PVC drain for both that will drain to either the sewer or septic. If there is a vertical piece to this, as there is in my basement, then you actually get some dribbling and running sounds from the water 'falling' down that vertical PVC. I get this same noise from the washing machine on the main floor draining down to the basement.
If the toilet is continuously running, you need to replace the flush valve assembly, or part of it, in the tank. If the flushing sound itself bothers you, you might be able to buy styrofoam insulation to line the inside of the tank. This will reduce the noise a bit while the tank is refilling, and will also reduce condensation on the outside of the tank during humid weather. Consider also replacing the toilet with a newer low-flush type. These flush quickly, refill quickly and use considerably less water, and are often quieter in operation than old-style toilets.
You are probably hearing the hot water hitting the cold pipe which causes expansion thus the pinging sound. Drain speed could probably be clogged vent stacks try cleaning them out.
In order for water to flow down a pipe, there must be a vent to allow the air to escape. Above a toilet, on the roof, there is usually a pipe or a vent hood, which is connected to the drain pipe. When the toilet is flushed, the sound of water draining can be heard issuing from this vent. In addition to the above answer, the air rushing through the water may be the cause of the gurgling sound, which is the air escaping through the vent to prevent the build up of air pressure inside your water system.
Bad fil valve