Does anyone know the best (and most economical) way to mitigate this noise WITHOUT putting in a carpet upstairs? 

@Adam Adams3 appartment buildings and 6 houses with 40k in hand121k gross income at say 10% annual that's 1,2m worth of real estate That's a 30:1 leverage...or 97% LTVI want the name of your lenderHonestly after the subprime crisis mess, i thought they would ban that kind of excessive leverage but it seems it is back to business as usual

Cris, I could not speak intelligently on those areas, as they are not where I focus.

Worse, what if there is a credit freeze due to economic conditions (e.g. 2009) and you can't get another loan at all?

Yes, it would be more economical to just have 2 bedroom houses, but you can score a grand slam every now and then with a big house that makes the higher cost worth it. 

For up to 12 months, and in some cases longer, life insurance companies can provide a firm commitment to borrowers that today’s interest rate will be the interest rate when they close, barring any substantial changes to the property and its economics.

It's a complicated topic, but there are 2 major economic factors that make them a super risky proposition. 

WHEDA (Wisconsin Housing and Economic Development Authority) has owner occupied loans you can use on a two family and actually put nothing down - at least they did last year. 

Disclaimer: My day to day income will be high enough for me to comfortably support the properties in any economic downturn, and I live well within my means.

DFW has strong growth and good economic fundamentals, but also a ton of competition.