Hi, Sorry to tell you that if your son has noise induced tinnitus then he is almost 100% sure to have noise induced hearing loss also. At present there is no cure for tinnitus although many people calim to get relief from various drugs, herbs and also zinc supplements, realistically you can only learn to live with it or develop a technique for ''masking'' it, such as playing soft music in the background etc...
suggest that you do a google search on tinnitus and you will lots of sites with info on the subject.