I have a howl noise coming from my Z at cruising speed, and highway speed. Its constant, no matter what gear I have it in, or whether its in neutral. I originally thought it was rear wheel bearings, replaced both. Noise was still there. Then I thought it was the diff. Replaced the open diff with an LSD (41k miles), the same noise it there. It seems to be coming from the rear. I can hear it from 40mph and up. At 45mph, there's almost a drone kind of sound. I spent close to $1000 and the problem is still there. Please help. Any ideas?

2003 350z Performance Ed.

 

 

Tires?

 

^ Tire feathering. Run your hand over the tires to see if it's smooth.

 

This is a very common problem especially on mud tires.




here is a very severe example of the issue

If your individual tire tread patches feel or appear to be at different heights this could be your issue

 

or the diff isnt shimmed properly

 

A lot of times, a noise like that will come from a loose front cowling. Check the trim around the wipers and make sure everything's secured properly.

(edit... Yes, I know you said it sounds like it's coming from the rear, but short of using a diagnostic microphone set to verify the sound source, don't count anything out. Cowling howling can sound like it's coming from all around you.)

 

U joints? They will make a bearing ish "whoooo" sound at.