I bought the sigma 50mm 1.4 in April after a lengthy period debating between this and the sony 1.4 50mm. It is a great lens and I have had many good shots from it - once you get used to the sheer amount of light it lets in! Anyway, this weekend it started to make a short burst of grinding sound just as the focus reaches infinity. It was slightly alarming so I emailed sigma who came straight back to me saying to send the lens in and they'd look at it. I've boxed the thing up and am sending it off tomorrow - has anyone else had this experience, or know what causes it?
I'll keep you posted on the quality of service/repair when it comes back.