06 Malibu Maxx LT Braking troubles

Hello! I bought this certified pre-owned from a big, reputable dealership in October of 07 and not once has it ever, EVER given me troubles with anything. Not one single bit of this car has ever been problematic, which is just fantastic compared to my last car. I do, of course, have regular maintenance performed on it (never missing oil changes, had fuel induction service done at 40k like it suggested, etc) and as such, I had the front pads replaced less than 3000 miles ago. It is after the front pads get replaced where my problem begins.

Well, I must admit that even though the braking was much improved after getting new pads (the front pads were almost completely worn down), it wasn't quite as responsive as when I purchased the vehicle, but I let that go for the time being because I assumed that the rear ones maybe are wearing thin, but I didn't have the money at the time. This past weekend, I was driving and I noticed a grinding sound that I could practically feel through the pedal. It did this several more times, and I noticed that the pedal travel was longer than usual. I figured that maybe the rear pads do indeed need replacing, so I planned for an appointment on Monday.

However, I noticed on Sunday that it wasn't making that grinding sound, and the brake force was reminiscent of how it was after the new pads (if not exactly the same force as before). Later on that day, I noticed it grinding again and the pedal travel was slightly long. I had the dealership look at it the next day and he turned the front rotors and said that it should take care of the grinding (it was covered by the warranty). It seemed okay afterward, but now today it was once again making a grinding sound periodically. Coming home after work tonight, I noticed that the pedal travel was drastically lower than the other instances. When I would brake with it, the amount of travel necessary (though not all the way down) was very startling.

I will have to see how it does tomorrow, but I figure that I should have them look at the car again regardless of if it does this again or not. Even so, I'm posting here because I'm curious. Do any of you have any theories about what could be causing this? People always assume its because they are wet, but we haven't had any measurable snow for a long time (the car does sit outside) and the sound/sensation of this is not a new concept to me and as such, I can confirm that this is most definitely NOT the case here. I plan to leave it with the dealership, describe it in detail more than before (instead of just commenting about a grinding sound) and pick it up later. If they claim to fix it and I find that this is still occurring later on, I will then take it to a different shop and see what their opinion is.