SORTED! I have had a bad "urine" type smell in an upstairs bedroom. Checked the cavity, no mice or squirrels! It turn out to be the UPVc double glazing. The bottom seal was letting water in from internal condensation. This collects in a bottom drip tray (under the glass and seal) and after time, STINKS! When the sun warms it up it smells more! I popped the bottom runner off, cleaned it out and all is good. Hope that helps.
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