Worn out rear brake pad only on 1 side...

The problem with the rear brake is most likely with the caliper assembly. The one that is wearing out too fast is probably dragging too much (not releasing properly). I would recommend replacement of that caliper assembly. As far as the "grinding" goes, if you are referring to a noise that occurs when you push the steering wheel into the stops and hold it there, then yes, any kind of squeal or grind in that condition is normal. If is does it when actually driving and just turning right or left more that a few degrees, then there may be issues in the power steering pump or rack assembly.

the noise is probably the ware sensors on the brake pads making noise the noise lets you know that the brakes are getting thin are are ready to be replaced.if you let this go to long you can damage the brake rotors, make sure you check to make sure the caliper is not sticking on the left side being this side is making more noise ,a stuck caliper can cause premature brake pads ware .

Most probabally the rear brakes are worn off. Take the wheels and brake drums off and check.

Have the rear brakes inspected. These are real easy to change if they need to be. You need to look under the car just outside the differential. This is an inboard brake system so the wheels don't need to be removed.

I have same problem; turns out all Honda Accords of this generation (2003-2007) do this. It has something to do with cold brakes and unseated pads, and the first time you stop from medium speed, you will hear a grinding, maybe from the back of the car (i think in my case).
My girlfriend looks at me, and we both wonder what it is, but it goes away in about 1 minute and I've realized it's only when the brakes are cold and it's not a problem. My brakes are basically ok, and there is nothing to fix...
I've done enough reading about this car on the internet, I feel pretty sure everybody's Accord does this, so I stopped worrying about it. A real problem, the sound would not go away as soon as the brakes warm up and seat the pads. After that, the breaks work fine.
If it was worn pads, the squealers will start up and not go away quickly. If it was a worse problem, the sound would grind continuously until fixed.
The two major problems with Honda Accord brakes are: 1) Brake judder at hi-speed medium braking. If you are going downhill, and just want to slow the car a little, if your rotors are getting worn, the steering wheel will give you feedback as brake judder. Hit the brakes harder, it will go away but it's scary and requires the rotors be replaced with a much higher quality rotor than came from the factory, and probably want to use ceramic pads (like Bendix CQ or CT). 2) Back brake pads wear down quickly. I read about this constantly with Accord owners, the EX back brakes are smaller rotors and pads than the front, but the electronic brake distribution system of the Accord will balance brake force between front and back, so the front pads will actually last longer than the back pads! This is very unusual but entirely normal for this car. Most cars are the opposite but that may change as we see new generations of cars with more evenly balanced braking front to rear. Be ready and watch your back brakes closely. Mine were toast at 30k...
I replaced my back pads and rotors, used cheapest new rotors I could find, and ceramic pads, and they have lasted considerably longer than the first set.
I now have 92k on my 2004 and the original front brakes are ready to be replaced. I replaced back brakes at 34k I think, and was very surprised they needed replacement at early, but the new pads have gone almost 60k, but look ready to be replaced sometime this year I think.
I have bad judder on high speed braking, but the pads are still ok in front. Rotors are **** in front and I'll replace with Centric Cryo-Stop rotors, they should last a long time as long as they get put on straight and I don't let anybody warp them with an air gun at the tire shop...
Two other more minor problems to watch for on this car: 3) Inner pads may wear faster than outer pads, because the caliper is on the inside, and forces the outside pads to contact the rotor after the inner pads are already braking. Seems like all Accords do this at least a little. The inner pads are not easily viewed without removing wheels, so it's hard to tell, but if your outer pads look like they are starting to get worn down pretty well, chances are good the inner pads are even more worn and you are ready to replace pads. 4) Pads may wear faster on one side of the car (fronts) faster than the other side. For example many people report driver side pads wear faster than passenger side. And the reasons proposed have to do with fast stopping for right hand turns or freeway loops. The car spends more time being braked in a right turn than a left over time.. But of course, on my car, it seems to be the opposite. The passenger side is wearing faster! Go figure..

That's to be expected and is completely normal.

Rear brake shoes as fitted to drum brakes can typically last up to 60k miles with periodic adjustments, but you have rear disc brakes and the shoes will typically last half of that.

Also, modern brake pads no longer contain asbestos and are now made using harder metallic compounds; the direct result is that brake discs (US=rotors) are also considered to be consumable items as they are worn down by the harder pads. It's not unusual to have to replace front discs every other pad change and rear ones with every pad change; in both cases the mileage will typically be around 30k miles on most models.

both parts will be cheap from brake pads to wheel bearing if need to replace. 50 bucks for sets of brake pad and wheel bearing will be 27 bucks. rear grinding could be your brake pads are worned and rubbing against the rotor. you can do the work your self and don't need a shop as long you have the right tools. if its the wheel bearing than its going to be other task, which still can perform the work at home. Big 1/2 inch sockets sets with box and open end wrench will come in handy. if it the rear end it will be best to take it to professional to have the work done.

Work the caliper piston in and out until it moves freely, otherwise buy a new caliper

Rubbing noise usually indicates that your brake pads has worn down, and it's rubbing against brake rotor. It's more like grinding noise rather than rubbing, right? And for the brake light problem, as brake pads wear down, brake fluid level goes down too. Your car is equiped with a brake fluid level sensor. So, check your brake pad first before adding brake fluid.