All four tires MUST be the same? (Yes or No?)

[CA777]

I just picked up my first X5, and the rear tires were shot, so I had the auto broker put a set of new tires on the rear. The tires that were on it were Michilin Diamaris, but because of the national backorder problem, and the fact that Michelin said they are not going to make that tire anymore, they asked if I wanted Latitudes instead, which were the closest match. The two front tires were fine, so I opted to leave them on. Hindsight is twenty twenty. First, since I bought OE 18's for a dedicated winter setup, I should have bought Toyo's for the sticky street set up, but I didn't think it all the way through. Second, the tires are incredibly loud, and there is a very noticeable tire growl when driving slowly and esp. when coming to a stop. New brake pads were just put on all four corners, so maybe it's brake noise as well, since the brakes are still wearing in? Third, I'm also hearing that on high-end, full time AWD vehicles, the tread patterns need to be EXACTLY the same on all four wheels, and the tread depth within 2/32nd's of each other, so that the grip and rotation is synchronized, and the differentials don't get out of whack, causing rough shifting. This seems a little extreme to me, since the contact patch on the front and rear tires aren't even the same size (staggered setup) which IMHO would have a greater affect than the same tires but with different tread patterns. A buddy of mine just bought four new Michelin Latitudes for his 4.6 and they wouldn't sell him only two, even though he only needed two, for this reason.

So the question is: is this more of a theory, which helps Tire Shops sell twice as many tires? OR, is this a bona fide fact, and I need to go buy two new Latitudes for the front ASAP...?

Thanks for your help; I apprecaite it.