Grinding noise while driving

Question

On my Opel/Holden Astra H (150KKm, front wheel drive, m32 6-speed manual transmission) I hear a slight grinding noise from the right-front, starting at about 40 km/h. The noise is synchronous to the vehicle speed, independent of engine rpm. It remains the same if I press the clutch, change the gear or switch to neutral. It also does not change if I make turns. The best description of the noise would be the sound of a steel brush pressed against a turning shaft. What i am not sure: There is a possibility that the sound would be more silent while accelerating.

So the possibilities would be: The differential in the gearbox, the intermediate shaft bearing, the CV joints of the axle, the wheel bearing or a slightly seized brake.

I tend to exclude the wheel bearing: Because the noise remains the same when making turns and the wheel bearing has no feel-able play when I jacked up the car and shacked the wheel.

When turning the wheel by hand I cannot identify any irregular sound.

I would appreciate any ideas on how to analyze the problem.

Edit

Just the following updates:

• The pads and rotors are new.
• There is nothing that rubs on the wheel.
• The boots are intact and not leaking.
• The transmission fluid is new. The transmission has a bad reputation for failing early (wrong bearing preload in the factory).
• The sound does not go away when tipping the brake
• The sound is very faint on the first km's and gets louder after about 10 km.
• I observed that the brake makes a slight periodic grinding sound when turning the wheel, always on the same position (perhaps a slight side run-out) but i doubt that this would be the issue. I will compare it against the other rotor.
• In the next day I will remove the axle from the wheel bearing and check the wheel bearing, the intermediate shaft bearing and the cv joint
• When changing the brake pads I lubricated the guide bolts. The next day I found out that the bolts should be mounted dry (ATE brake system). Perhaps the rubber bushings surrounding the bolts swell in combination with the grease. I will change the bushings this week

Answer 1

The diagnosis that you're done pretty much narrows it down to something between the output of the transmission and the wheels, including the brakes. You can eliminate the brakes, by lightly applying the brake while listening for the noise to go away (it is the brake) or not (something else) – while driving.

If you're sensitive to the noises of your car it is likely that you'll catch something like a dry or failing bearing before it is so bad that you'd feel play or hear the louder noises that indicate a definite failure.

What I'd suggest is that you lift and block up the car and pull the front wheel(s) and inspect carefully. Some things to look for:

• Wear on the brake pads, you may be starting to hear the wear indicator doing its job.
• Anything in the vicinity of the wheel that could rub (or that could move close enough to rub at speed).
• Inspect the drive shafts for damaged boots and/or leaking grease.
• As Paulster2 suggested in the comment, listen carefully to the bearings. The sound will be very faint.

Since it is a moving noise and happens at a relatively high speed it will probably be a very faint sound when the car is on blocks (and may not occur at all if it requires a loaded suspension). So use the "screwdriver trick" (a video if you prefer) or a stethoscope to help you isolate the sound.

Another think you could try is to have somebody drive the car by you as you listen on a quite stretch of road. It may be easier to hear and isolate from the outside.