Help Diagnosing Car Hum

[SIB]

My 69 E3 has a humming noise that appears to be coming from the front of the car. I noticed it for the first time this summer when I was taking some sharp turns. After that drive, I did not hear the noise for a while. Now it seems to do it when the car is going straight as well, but only for the first several minutes of driving and then it mellows out. My thinking is that it's the rotors - does this make sense? I am not a mechanic, so any help is appreciated. Also is it somehting that I need to address now or can I put it off for a while? Thanks in advance.

[oiseaux]

Live long, drive well and prosper!

BimmerShifter since 1969; currently
'82 733i 5-spd, 318k miles
<img src="http://www.roadfly.org/bmw/gallery/photos/photos-10-2003/25-2560840.jpg" height=122 width=200>
'93 850CiA, 134k miles
<img src="http://www.roadfly.org/bmw/gallery/photos/photos-10-2003/25-1767127.jpg" height=122 width=200>