What does a raised IgG level and sensory hearing loss mean?

These may not be related at all. The first issue is that of IgG. There are five main types of antibodies or immunoglobulins known as IgA. IgD, IgE, IgG and IgM. IgM antibodies are the "first responders"when the immune response is raised and confers short term immunity whereas IgG serves as a "memory" antibody that confers long-term immunity. A high level of IgG indicates that the immune system is producing a high level of long-term immunity antibodies.

There are immune disorders that result in sensorineural hearing loss but they are relatively rare. Statistically speaking, these two findings are probably unrelated.