Nine times out of ten it happens when I'm accelerating from a stop or near stop (i.e., rounding a corner). That's also when it's the loudest. But even then it's not that loud although it varies in intensity. I've had it do it several times when I'm cruising along at like 35-40 miles an hour and I've got the gas pedal slightly depressed to keep it at an even speed. It's only happened twice while sitting still and then it was so faint I was not even sure that's what I heard. Oh, to answer your question I have a 4X2.
Thanks,
Hex