Smell from kitchen sink

Hi

I live in a flat on second floor.

There is a smell coming from kitchen....definitely the drains. The odd thing is if I put my face inside the sink I can't smell but I know its through that.

Sink is new, p trap underneath is new (comes with the sink), dishwasher and washing is new. But pipework it connects are old I would say probably 12 years and disappears somwee behind the wall.

No blockages and water drains smoothly.

Tried one shot, Mr muscle other chemicals in kitchen sink, bath and bathroom sink (they probably share the same pipe). When I pit these chemicals the smell disappears but comes back on few hours later.

Smell still there!

The smell isnt there when dish washer runs so what could it be?