You have not given us much to go on. It would be helpful if you could:
1. Provide a structure
2. Provide details of the method of preparation (for clues as to possible impurities and side reactions)
3. Post spectra (13C would also be useful)
Initially I was going to suggest the possibility of rotamers, but if both peaks integrate to 9H, then this is not the case. Do you see peak doubling anywhere else?
Have you checked the literature to see if in is a known compound and that your data matches?
Do you have mass spec confirmation for one Boc group?