If the IRS states that it is mailing your check instead of direct deposit, most likely the reason is that they tried to directly deposit the refund into your account (with the banking information that was provided on the tax return) but your bank rejected the deposit. First thing to do is to call the IRS and find out if they are actually sending you a paper check or if they are planning on directly depositing your refund. If they are sending a paper check they I would call your bank and see if the IRS sent a direct deposit and if it was rejected and if it was, why.
If you refund is over $10,000 the IRS states it cannot directly deposit the funds into your account, but need to mail you a check.
Unfortunately the IRS does not share any information regarding direct deposits with Turbo Tax.