Hello and welcome to Just Answer.
The damage is already done. With an all wheel drive vehicle when you replace tires you need to replace them all. The circumference of the tires all need to be the same or at least very close. Most within 1/4 inch or less. If the transfer case is making a noise now the driveline wind up that occured from the different tires has cause damage. Replacing the rear tires now more than likely will do nothing for the noise. You may be able to check the transmfer case fluid and see if it smells or looks "burnt". if it does you can change the fluid and see if it helps, but in my opinion and experience once the noise occurs it is to late.
Sorry I was doing some research while I was typing. That is why it took so long.
That sounds about right. i just looked to see if there was an aftermarket available and none were found. The only other option would be a used one. Let me see if they are available.
They are available used. Apparantly it is the same as a Toyota Highlander also. Here is a website that you can check your area to see if any are available. If there is one out of your area they will ship to you also. www.car-parts.com
Just put in your vehicle and select transfer case from the drop down menu and it will list them.
Not a problem. I am sorry to hear about your problem. Make sure you put the rear tires on before you fix the transfer case.