What Happens to Frequencies Above the Nyquist Limit?
Sounds above the Nyquist limit (in this case 4000 Hz) will seem to fold back into the allowed range. For example, a tone 100 Hz above the limit will appear as a phantom tone 100 Hz below it. So a frequency of 4100 will seem to appear at 3900, one at 4200 will appear at 3800, and so on.

This is called 'aliasing' or 'folding'. The apparent 3900 tone is an alias for the 4100 tone. Since actual, complex sounds are composed of many frequencies, the audible effect is not as clean as theory describes it.