Feeding rats to walkers is crazy but it wouldn't attract any others. It's not like they can call out to each other and say "Hey, someone opened up a rat restaurant down here!" The mere fact that anyone was there at all would be what attracted the first ones, then the noise would attract others. Walkers don't have enough intelligence to hang around waiting for treats.
One thing I do wonder is why the walkers have to eat at all since so far I haven't seen any evidence that they starve to death if they don't. It seems more like they are driven to murder rather than to eat and their teeth are their only weapons. But that doesn't explain why they hang around to eat their victims once they are dead. I guess some questions are better left unanswered so the show can go on.
Good observation, now you can enjoy the series.....LOL!
As a side note, don't get caught up in the "they should have done this, they should have done that, they should have found a tank, they should have found etc.....etc........."
The show is what it is and the writers are going down the right road...........
It was established last season that they do actually burn calories and can starve, it just takes much, much longer than a living person.