I currently have a tenant residing in the lower lever, and am considering getting carpet in the rooms above the tenant to deaden the sound (footsteps, loud noises, etc.)Would you recommend carpeting over the hardwood?

Make sure he/she checks the following:1 - Furnace makes a "coughing noise"2 - Temperature in the house seems to be "feverishly" higher than it should be3 - The furnace fan doesn't seem to be moving/replacing the inside air as well as it should so the house doesn't seem to be "breathing" like it should. 

Keep giving them 3 day notices to quit making noise or whatever else you can think of that would be legal and related to what they're doing and that violates your lease. 

We don't allow dogs in our upstairs apartment above our commercial building because the flooring is hardwood and it causes way too much noise.

It may be that noise transfers easily through the units.

If anyone needs advice on anything to do with aviation (low flying planes, aircraft noise issues, etc) let me know, that's my speciality!!

And really, if you were looking for a place to rent, would you be happy to rent a place where the landlord is going to be there making noise after you move in, putting in landscaping?

You'll get rattled by the institutions & the everyday tenant.  

I own an upper/lower and it can be loud for downstairs and been contemplating putting carpet in the bedrooms in the back just to deaden noise for privacy.

That is all just noise.