2001 Mitsubishi Montero Changing engine oils

I have been using the same conventional oil for the past 13 years (switched to high-mileage a few years ago). In December, I was convinced to try the Eco-friendly high mileage oil. Noticed a change in the way my car sounded within a day- a louder whirring noise upon acceleration. Didn't pay it much mind, but more recently the whirring noise has become louder and more strained, especially when accelerating. I've never had this problem before, and only noticed it after the oil change (the rear differential was also changed at the same time, but I'm assuming that's unrelated?). Could it be the new oil causing my car to sound much louder and more strained?