I moved into a new house 5 weeks ago and there is a smell from the en-suite. It is a cross between sewage and musty. Nothing is blocked. If the window is shut overnight it's bad in the morning. Occasionally there is no smell. I have had the area around the toilet re-sealed. The drains outside stink - i have contacted the water board - but i am the only person who can smell a bad smell indoors. Nor do they smell the same really. I have looked at other posts on the net - is this to do with a soil pipe and vent?
make sure the vent is not blocked,this smell can happen when you have ensuite and bathroom it can be poor pipe layout
also check the outside manhole cover to make sure its not blocked and try to get someone to flush the toilets while you watch the water flow thru the sewer
You may have a problem with the syphone effect from a sink or bath in that room or possibly another room on the same floor, basically if you fill the sink or bath then remove the plug it can syphone the water for instance out of the shower trap(plug hole) this will then allow foul smells into that room, to test in the morning you will need to smell the suspect trap usually the closest one to the floor (shower). Alternatively pour a glass of water down the shower trap after you have your last wash/bath in the evening, if no smell exsists the next moring chances are you have the syphone effect. To cure this you can try getting a plumber to fit an air admitance valve to the waste pipe nearest the shower this should solve the problem.