I'm now thinking that the neighbor's retaining wall, which is quite substantial, may be the root cause of the problem. 

Some older buildings the trees were planted to close to the buildings for the height size and can cause roots in utility lines, sidewalks popping up, animals access to the roof, cracking the foundation, etc. 

@Kurt K.I don't live in Nashville, nor do I have any valuable information to share with you, but I used to live in East Tennessee (Knoxville) and am just rooting for you.Good luck on your house hacking endeavor and keep us updated!

@Brandyn Whitacre finding the root cause is important. 

Who are you rooting for?

It's free for you and they root out a lot of fraud.

Obviously this only works if the rent from the first place will cover the HELOC expenses, or if you can simply support both monthly payments that works also.Let me know if I missed the point here, would love to help, just feel like I'm missing the root of the issue.   

I suspect this is the root cause. 

I don't sense that at all right now, but that feeling takes time to root in a market.  

I have learned to plant the seed and hope it takes root!