I moved into rented house last year, and no matter what I have tried I can't get rid of a musty smell. I have cleaned carpets, used bicarb soda, and so on. Any ideas anyone?
Unless you can detect the source I don't think there is much you can do. I had the same problem in my old house and could never figure out where it was coming from.
Open all the windows for an hour or two and let fresh air blow thrugh, do not hang stuff out to dry indoors without ensuring fresh air can blow through. Make sure you have no damp patches maybe caused by leaks in pipes or the roof and if you do then treat them.
I would try using a burner or a diffuser and one of the following essential oils,
Eucalyptus citriodora, melissa, or citronella mixed with rosemary . You might need to use it a few hours a day in each room and about an hour afterwards air the room but after a week of so you should get on top of it. You can also damp dust with water with a few drops of each oil . if you use synthetic spray air fresheners they can leave a musty scent after a few hours.
Try cutting 3-4 large onions into quarters and distribute throughout the house. This should quickly neutralise the smell and possibly permanently reduce it. However, by far the most likely cause is too little heating over prolonged periods so you also need to make certain the place is heated. Get a humidity gauge and if the humidity is above 65% increase the heating - and not just for a couple of hours per day, more like permanently.
IMO You need to address causes of your damp, not mask it with air fresheners etc. Just fresh air blowing through may help, open front and rear doors and windows for day or two. Is smell only on ground floor?
'Ground floor' - might be from the drains. Make sure all the wastes in the sinks are full, use a rubber plunger to clean the u-bends or remove them to clean. Squirt disinfectant into the overflow holes in the sinks.