I have a 2002 ETC/ECS with about 52k miles and it has a low pitch kind of roar or whine that becomes most apparent at and above 35 mph and the frequency of which runs with the speed of the car rather than the rpm of the engine. It also kind of cycles with the tire rotation, kind of like wu, wu, wu, wu. It seems to come from the front, but when I turn my head it pretty much comes from anywhere under the car, but still seems mostly from the front. It isn't the front wheel bearings because I replaced both of the front hub/bearing units and the sound is still there. I'm still wondering about the rear wheel bearings, but the sound does not change when turning and loading one side or the other. I think I'll change the rear bearing units this weekend anyway, but I am now wondering about possibly something else like the CV joints. Any other ideas? Thanks. I'm new here, but I am not new to Cadillacs or to cars generally.

 

I changed both of the rear wheel bearing hubs and it didn't help a bit. I could pretty much tell that when I took each of them off because they felt very tight a smooth when turned by hand.
I guess I should have said in the title to this thread (?) that the noise is in the running gear or final drive train. Now I am pretty sure it is coming from the front and I think it has to be at the final stage of the trans or in the CV joints.
Not much help here or anything going on in this Forum, I see.