Strange wooshin noise when I open the window from the side of the house?

This has recently started happening since we turned the boiler in the loft back on what I can hear is like a wooshin noise only when I open the window like the toilet is being constantly flushed we have had a new toilet fitted and it shuts off fairly quick it's like hearing the sea crash against the window but I dont hear it inside the house? What could be causing this?