99 monte front end growl

'99 z34, 3.8, 70k miles.
Left front growl at all speeds, road speed related.

It started a couple of weeks ago, barely noticeable. It has become slightly more noticeable now & sounds very much like a heavily feathered tire. I would guess the rhythm to be 4:1 or 6:1 for every tire rotation. It goes quiet when turning right & is not dependent on braking, accel, decel, engine speed or trans shift. Still there engine off and coasting. Most noticeable at around 35MPH, but can be detected right up to full stop. I can even feel it slightly when it is at its worst, like a worn differential that isn't meshing properly.

Tires are in good shape, and swapping them left for right did not change the location of the noise. Simple... left front wheel hub, right? Well, a brand new Timken unit did nothing for it. That leaves me with only the half-shaft or output transmission area to suspect. The growl seems much too rapid to be a half-shaft (which appeared in good order visually) in my mind and I know of nothing in the tranny output that could make this type of noise.

Any ideas?

Maybe the other side, jack it up and run the car at low speed, safely of course. See if you hear which side it is.

Yea, that's my next move... once I find a volunteer to man the brakes. I started to climb underneath once, but I wasn't too keen on getting that close to all of that rotating hardware by myself, even with a long probe. That and because it tends to wind up pretty high just free-wheeling... too much noise to hear well when there is no load on the drive train.
Thanks MW, I appreciate your input.

OK I admit it, I'm stupid. I was so certain that I was hearing the noise coming from the let front that I forgot the golden rule... "Quiet turning right, the right side is the right one."

With no volunteers to help man the helm while I climbed under for a "while running" diagnosis (and in light of my realization that I am stupid!), I bit the bullet and replaced the right front hub on faith. She's quiet as a church mouse now. This isn't my first rodeo, so noise transference isn't new to me, but this one still surprises me. The noise was so clearly coming from the left. I never would have found it by climbing underneath anyway as it turns out. Without a load on the bearing it was much quieter than the rest of the drive train. I found that there was no noticeable play in the assembly while mounted. Once I had it off I grabbed one of the lug studs and rotated it nearly as fast as I could... I could just make out the gentle "tackita-tackita-tackita..."' of a bearing starting to go bad.

Any way, here are some tips for those who might decide to give this a go in your own garage. Since mine is a '99 Monte, I'll focus on it - it really isn't a bad job at all. You'll need a well stocked box of standard tools and a couple of special ones: 36mm socket for the axle nut and a T60 torx bit to remove the caliper bracket bolts.

First, read this well written account from a home grease monkey like most of us:
http://www.paulstravelpictures.com/GM-Wheel-Bearing-Hub-Assembly-Replacement/index.html
Even though it focuses on a 2001 Grand Prix there is a lot of good info and photos for late '90s through late 00's.

The biggest tip I can give relates to the caliper bracket bolts. These things are nearly welded in place, so standing on your 24" breaker bar won't do the job if they are still in place with loc-tite. In my case (a few years ago) I securely settled the vehicle on two jack stands with a floor jack under the main cross member for extra support. After removing the wheel and caliper, I used a second floor jack to put torque on my breaker bar. The car literally lifted a good 2 inches off of one jack stand. While I stood there thinking "Holy Crap, now what?!?" the car slowly dropped back down and the bolts came loose. Just let the weight of the car do the work... but BE CAREFUL!!! There is one heck of a lot of tension there... if the breaker bar were to slip or snap there is just no telling which direction the pieces might fly.

Another biggie is: PUT THE ROTOR BACK ON BEFORE YOU RE-INSTALL THE CALIPER BRACKET!
(sigh) I hated having to take that bracket back off. Did I mention that I'm stupid?:rofl:

I would also recommend a little WD-40 on the exposed ends of the wheel hub mounting bolts to help cut the grime and rust when you start backing them out. Beyond that, I only needed a little patience. 2 hours got the first wheel hub replacement completed. About 1.5 hours on the second one.

One last little tid-bit: the mid to late '90s hubs don't have the ABS molded in. The sensor and exciter ring are separate, so you don't need to worry about them.

Hope this helps!

i have a 05 impala that is doing the same thing that you describe only i cannot get the noise to let up by turning or coasting the sound to me sounds like it is on the left front hub/wheel area when ever i have a back seat passengers they say it sounds like it is in the right rear thanks for the info it is some place to start have a good day