I isolated total RNA from rat muscle using Trizol. I had 2 samples, one from one leg and one from the other. One looks fine in a 1% agarose gel (3 rRNA bands) but the other one only has 2 rRNA bands! 260/280 ratio was 2.0 for both samples.
I believe that the 28s band is difficult to visualize if you do not load enough RNA onto your gel. It should appear diffuse anyway if you load it onto a standard agarose/ethidium bromide gel but sharp if on a denaturing gel. You should load at least 500ng of total RNA.