What's that noise???!

So I'm sat at the laptop enrolling for university and facebooking etc and i keep hearing this buzzing/vibrating sound. Check my phone: nothing. So I leave it for a while. I can still hear it and it's starting to irritate me. I get up look around for my sister's phone. Find her blackberry, unlock it, and still: nothing. I sit back down but I can still hear it. I try to ignore it and dismiss it to be some sort of garden equipment a neighbour might be using. I know it can't be my Dad's phone cos his phone is always on loud not vibrate. Plus who would be so persistent to keep calling after all that time?! Ten minutes later I finally realise: it's my Mum who's on the sewing machine downstairs!!