What's causing this smell?

[addler]

Yesterday I noticed a bit of a musty smell coming from our bathroom. I thought it might be one of the drains so I put some drain cleaner down the sink and the bath and the smell seemed to go away, but a few hours later it was back. I can now also smell it in the en-suite, which is on the other side of the family bathroom wall.

Any suggestions? I can't see any obvious leak coming from anywhere and there's no visible signs of mould. It came on very suddenly as well. And why would it be in both rooms? Sometimes the en-suite toilet makes a noise or the shower drain bubbles up when someone used the family bathroom, if that's relevant.

Any ideas of things to try very welcome, before I call someone out to come and investigate a hidden leak I suppose.

We had a similar problem and we could not figure it out for years. Drain investigations showed an uncapped pipe beneath the flooring where sewer air would sometimes drift in. Once the pipe was sealed, no smell.

That sounds horrific!

We had a drainy smell for weeks and turned out to be the downstairs shower which is never used and the trap was dry so letting up drain smells - i just top it up with water every now and then.

I'd do a drain cleaner again, it might have just shifted it a bit but not all the way.

The bubbling sounds like a blocked drain/ pipe to me. Have you checked your inspection chambers outside, to rule out a problem in the sewer?

We get the same thing in our ensuite shower and just have to top the tap up with water every once in a while.

I have this and our plug in the basin is one of those pop up ones and it gets a bit manky every now and then
A scrub with some bar keepers friend and a kettle full of hot water does the job

Pour an entire bottle of Caustic Soda into a bucket of water, mix, then pour down drains. Make sure you wear gloves though and open windows! That stuff is.....well, Caustic!

Right off to scrub and pour. Many thanks!