Test results came in suspiciously high (and fast), so I hired a professional radon testing company.  

Ugh.I even spoke with an investor who I connected with through BiggerPockets because we both happened to find the same suspicious kind and philanthropic, extremely wealthy human who would love to offer lower rates to borrowers who could not get financing elsewhere. 

But when they feel the need to say that, it makes me a bit suspicious.

I'd be suspicious of a German Shepard only growing to 40lbs.

As always, I would suggest speaking with legal counsel to better assess the practicality of doing so, yet my suggestion would be to consider keeping the Ownership Interest the SAME as seen on the paperwork when you purchased the property (ie. 100% Ownership Interest in [Enter LLC Name here]) to avoid being flagged for suspicious activity and provoking the enforceability of the Due on Sale Clause. 

They basically demand a solid paper trail showing that the HELOC (or any other) funds were used for this business and for nothing else.Your mention of $100k makes me slightly suspicious that you've been looking at the now obsolete option of deducting a $100k HELOC as a personal itemized deduction.

I’m also suspicious (partly what’s keeping me from getting anything at all) because the mortgage would come to $1500-1600 at 7%+ interest and comparable rentals in the area are listed for $1900-2300, but that seems too good to be true.

Never heard of it, but after looking at their website, I'm immediately suspicious of anyone claiming you can replace your 9 to 5 with this one simply hack.

This makes me a little suspicious...

I was suspicious of the intent behind that question ("What do you plan to use the HELOC for?").