2002 E39 525i 5-speed with the M sports package (but it's not an M car - and this info used to be part of my signature with the old site...anyway...) - @140,000 miles on 'er. Over the summer I replaced the tires with a set of new Michelins (Primacy mxm4's). They are speed-rated for this car and fit/ride like they were meant to be together! Lately I've begun to hear a strange noise, sounding like a lawn mower, at crusing speed (@60-80 MPH). I don't notice any power or MPG loss, don't notice any leaks or engine issues (no smoke, sputtering, hesitation, etc.), the car seems to be running normally (save for a slight increase in road noise but I thought that would be normal after tires are a month old). That is, except for this "lawn mower" sounding hum. I do notice that when I take my foot off the gas but maintain my speed, I do hear the sound...so again, I don't believe it's engine related but...I don't have that kind of acumen to be able to know for sure. Questions abound...could the tire(s) be rubbing on something, could there be something loose, is it an issue related to alignment or bearings or some wheel-related issue, or do I have a problem with the engine after all? Any and all ideas/thoughts/replies will be most appreciated...thanks!