No, personal loan interest is not deductible even if it is for a rental. The loan must be secured by real property.
A secured debt is one in which you sign an instrument (such as a mortgage, deed of trust, or land contract) that:
Makes your ownership in a qualified property security for payment of the debt,
Provides, in case of default, that your qualified property could satisfy the debt, and
Is recorded or is otherwise perfected under any state or local law that applies.
In other words, your mortgage is a secured debt if you put your qualified property up as collateral to protect the interests of the lender. If you cannot pay the debt, your qualified property can then serve as payment to the lender to satisfy (pay) the debt. https://www.irs.gov/publications/p936/ar02.html#en_US_2015_publink1000229890
