I need to hear the sound as well as examine the child before come to conclude that he is having downs syndrome.
But at around 7-10 months child makes some noise which known as cooling and which is totally normal. It's part of speech development. If your child's development is normal and no other abnormalities and both parents age is not more than 35 years then it is less likely to be downs syndrome.
Next Steps
consult pediatrician, get examination done by him and if there is few abnormalities in examination then doctor will advise chromosome study.