@Roberto CostaI just wanted to inject a quick reality check, not just for you, but for all investors who are thinking about complaining about rates.In your case, to put things in perspective, rates in the 5's for a non owner occupied property with just 15% down is not high. 

Your partner could inject money into the LLC in the form of an equity injection.

Not surprising.Large PE firms are already ‘flipping” although they like to call it ‘when we see an asset that only needs a small equity injection of 20 thousand or less that we can sell for a high profit then we do it.’

Lower asset classes may have older buildings which may require more frequent upkeep, however the cash flow could be much greater than a higher asset class just due to the lower capital injection at the start of the process.Just make sure to account for all of your numbers when running a deal, and don't forget to add in number for maintenance and capital expenditures, because most people who don't account for those things are just fooling themselves. 

You can also hang the ceiling sheetrock using resilient channel which will further reduce the sound travelling through the assembly.I would not inject close/open cell foam into the joist cavities - where the assembly is a fire barrier, it would be neither appropriate nor permitted.  

Would a little cash injection boost it?

I am setting up a LLC with a capital injection of a $480k from a free and clear property from an investor with a current buyer.

I currently have a potential capital injection of a free and clear house at $420k.

Wholesaling is great for one-time cash injections, but it still leaves the majority of the opportunity in the deal for someone else to benefit from.

Solid strategy, and it probably will need injections from you and your partners though to actually grow as quick as you want it.