In the interests of full disclosure, I should say that I work for one of the big milk producers. I wont say who and I wont name any brands.
Having said that, I would take the product back. If you can smell it, the odds are there is something not right with it.
Unfortunately, there are a number of places along the chain that can effect the product.
It might be the brand, it might be the batch, it might be the milk handling procedure that happened for that delivery.
I have noticed it myself with one particular store, and product. I have bought the same product from other stores, no problems, but from this one store, SEVERAL 2LT bottles have gone down the sink after making one flat white with it. Very similar to what you describe. I could smell that it wasnt right. It wasnt OFF, but it wasnt right. We no longer buy our milk from that particular store if possible, and Ive not experienced the same issue anywhere else.
So I say mention it to the place you bought it.
Personally, I mentioned my experiences internally at work as I felt it was a conflict for me to talk directly to the store.