Keep working with the dealer until they can pinpoint the source of the noise (I am assuming you still have warranty--if so, take advantage of it). Here are some things I would suggest. If you think it is tires, ask the dealer to switch the tires with a similar vehicle (hopefully they can find one that has different type of tires). Sometimes the Original Equipment tires on vehicles are not the best, most premium tire on the market. Manufacturers buy tires in bulk, and they are forced to compromise between cost and quality. So, often, an aftermarket tire (Michelin is one of the best) will make a significant improvement in ride, noise, and handling. The dealer should be willing to work with you on this. But, if the tires are replaced under warranty, they will want to use the original type tire unless Nissan allows otherwise under warranty. Sometimes, changing tire brand will be covered in special cases where a customer has complained enough about noise. Or they may offer to split the cost of new tires with you. Otherwise, you might get stuck with the cost of new tires if you want to experiment with a different brand.
Also, ask them to let you drive a similar vehicle with the same transmission and tires, so you will know what a typical Murano feels like. If they are trying to claim the noise is a vehicle characteristic, make them prove it by doing a side by side comparison. Your car is relatively low mileage, so the comparison will let you make a fair judgement about what is characteristic and what is not. Sometimes the vehicle will change a little as it gets some miles. But generally, your vehicle is still young and should still feel pretty much like a new one.
If the tires are not wearing smoothly, they could make a noise. The wear should be smoothly even across the tread, without any sawtooth type "feathered" edges on the blocks of tread. Noise will be worse if the tires have not worn smoothly. The vehicle might need some fine tuning of the alignment to reduce tire wear.
I have a hard time believing they would replace a part for a noise, and then declare it characteristic. If the noise was bad enough to replace the bearing, and it is still unchanged, then something is probably not right. The CVT stands for constantly variable transmission. It operates differently than a conventional transmission. The CVT adjusts its gear ratio constantly to keep the engine at its most efficient rpm range. The feel is unsettling to many people since the engine speed basically stays constant. There is no rev up, shift, rev up, shift type feel. In fact, many of the CVT's coming out now have been calibrated to let the engine rev up and imitate the feel of a conventional automatic--just to make it feel more like a typical transmission. They had to do this so people wouldn't complain about it feeling like the transmission was slipping.
I hope this gives you some insight. If this answer is helpful, Please press the Accept button. Thanks!
Service Engineer
Master Tech, Bachelor's of Science in Automotive Technology, Ford Factory Trained