Is the leading zero required? If it is and you are using a template excel file and not a new file then set that field as text in your template file. If you are not using a template file you might want to.

As I understand it the first row is sampled in the result set and if a leading zero is found then it treats it like text and adds the single quote. If the leading zero is not required you can also cast or convert in the sql statement so that the number is treated correctly.

I have had this same problem and while I think the explanation is a little odd that SQL treats a leading zero in this way I do find that either of the two steps I mention have fixed it for me.