When does baby turn head to source of sound out of his sight

My baby is turning 3 mth soon. When i ring a bell out of his sight, he did not turn his head to the sound. Most websites states that baby should achieve this skills at 2 months. But I look through his health booklet and noticed that it stated 95% of baby will turn by 7.5 mths. Should i be concerned? When did ur baby turn their head to source of sound? When does polyclinic check on this skill?