This problem carried on for a full year until I nagged Husband to really DO something about it! The result was we hired a cherry picker device (quite good value we thought) and our lovely next door neighbour who has a head for heights and building experience zoomed up to the window - luck was with us - it was a horrible cold windy day with the wind coming from the north. He could see nothing but raised himself above the window and lo and behold he discovered the window had not even been sealed in properly by the builders!!! The wind had been vibrating against a piece of waterproofing lining. Neighbour cheerfully sealed up the window and all was well - until last week. A familiar moan started again - oh no, not again.
I had a brilliant idea - I bought some blue-tack, hung out of the window and squashed it into the recess above the window. Silence was golden. This weekend we bribed Neighbour to scoot up his own long ladder and re-seal the window (the sealant had dried out). So really, we have to persuade our neighbour not to move house ever so that annually he can renew the sealant for us! Why oh why do not builders check their own work. I would have been fired from my job if I had made such basic mistakes.
