Text/iMessage alert tone problem since ios5 update

Since I updated my 3gs to ios5 last week, when I recieve a text message or iMessage, the tone 'stutters' before playing. At first it was quite funny, after I had switched the handset off and on again, it stopped doing it for a few hours, but then started again. It's now quite annoying. Has anyone else had the same issue or can advise me on what to do to fix it? Many thanks in advance 🙂