Are you renting, or do you have a condo association? If you were free to remodel (I would remove the bricks, put the radials under them, and put them back), you could put an adequate radial field in at that location! I don't think I'd try an inverted "L," because you don't have much linear room for the horizontal portion; but I would definitely put in a trap vertical, fan vertical, or similar, to supplement your loop. About that noise level: if you can get the vertical away from the house, and feed it with a good choke (don't just wind up a few turns of coax and expect it to work well on 40 or 80m!), there is a good chance that you will see a perhaps one or two S-unit drop in noise level compared to a very low horizontal loop with the house inside the circumference of the loop, or one leg of the loop passing very low over the house. Well, in that case it has to be admitted that this antenna is working about as well as its going to. If you can be satisfied with it, then so be it. But you can do better if you want.