Humming when Driving Above 30mph

[RD1990]

Hi All,

I'm looking for some help with my car (A4 2.0tdi B8 Auto Quattro 2014 SE), I recently changed the front wheel bearings (as a hub assembly) in October 2023.  Mid-December I noticed a humming/winding sound coming from the front right of the car when doing 30mph or above, which sounded very similar to wheel bearing noise (no clunking).  This would get faster/slower with wheel speed, and is constant (not influenced by acceleration or braking).  I checked the wheel bearings again, and they seem OK.  I checked the tyres and the front right looked out of shape - I was confident the noise was this tyre due to the uneven wear.  I got two new front tyres fitted and the alignment done, but the noise is very much still there.  Despite the alignment being done, the car is still pulling to the right.  I looked further and believe there is play in the front drive shaft inner CV.  I'm not too knowledgeable on quattro and the differentials etc but carried out a few more checks which were recommended by a mechanic.  I put the car on a lifter and put the car in drive to see if I could hear where the noise was coming from, as I couldn't spin them freely enough myself.  At first all wheels started spinning, but the front right was intermittent.  Soon only 3 were spinning (the front right wasn’t - so I couldn't listen for noise!).  I put the car in neutral and spun the front left wheel - the front right wheel did spin in the opposite direction as expected.  I then put the car back in drive but held the front left wheel still, the front right wheel didn't start spinning (I’m advised it should have at this point?).  I have been advised to try putting the car on a lifter, in drive, but turning the steering full lock to see if the front right wheel starts to turn.  I’ve also been advised to try disconnecting the prop shaft to the rear and see if the car drives to determine whether it’s a differential issue.  I have attached a link to a video of the play in the front right inner CV axle.  My query is whether from the above, and attached video, is it clear it's the CV axle, or could it be the differential?  If not, what further checks should I do to determine what the issue is?  I’m thinking it may be easier to take the car in to a garage having tried everything I can. 

Thanks in advance, RD.

Link to Video

[RD1990]

Hi Jasonj, thanks for your quick response, I appreciate it!

1. I have, there is no play in the wheels when pushed/pulled in the 12 and 6 o'clock positions. 
2. There currently is no evidence of grease leakage on any of the CV joints - would it be safe to assume the grease is still there based on that? The outer CV on this particular wheel was replaced in September 2023.  
3. I'm unsure what you mean by "pushed to the right" but when driving with the steering wheel straight, the car goes to the right (so I have to have the steering wheel turned slightly to the left in order for the car to go straight).  
4. I understand the tyre was showing signs of cupping as the tread on the outside had worn patches every 6 inches or so around the circumference.  
5. I'm not sure if there is traction in the front right.  How would I identify this?  From the testing I've done recently, I have a feeling it's free spinning and relying on the other wheels to propel the vehicle.  

Thanks, RD.

[RD1990]

Thanks JasonJ, appreciate your assistance and detailed response. 

Your response makes sense and I feel is quite an accurate representation.  

In relation to your suggested prognosis, please could you elaborate on how an OBD diagnostic would identify whether the drive shaft or differential is the issue?  I'm not aware of these being monitored, apologies if this is a daft question. 

I don't believe the output flange is spinning either during my above testing.  Could it be that there is an issue with the CV axle, but caused by a problem within the transmission/differential?

Would a worn output flange bearing cause enough play for the teeth not to bite?  Is my following understanding correct - the output flange for the side in question is linked directly to the ring gear, but the ring gear must be working for the front left wheel to be spinning?  Unless, as you say, the ABS sensor is faulty causing the wheel to apply the brake.  During the testing, when the wheel isn't spinning, I am able to turn it by hand so I don't believe the brake is activated. 

Having said that, it's jogged my memory and I forgot to mention earlier - I have had a few recent issues with the brake on this wheel.  Two to three instances, a scent of burning when getting out the car - the disk and hub is sizzling hot compared to the front left wheel.  Maybe you are correct that there is an issue with the ABS, but would this cause loss of drive from the transmission/differential or could it have damaged something within?

Thanks again, RD.

[RD1990]

Hi JasonJ,

Thank you, I will see if I can get OBD looked at this week.

I will get in touch with a local Audi specialist and request a quotation - rather than take the drive shaft out and investigate further, I imagine they will advise if the CV drive shaft is faulty when carrying out their diagnostics.  

Thanks, RD

[RD1990]

An update on the above:

• Booked an appointment with a local gearbox specialist - earliest I could get is 22/03/24.  
• Took the car to get some fuel last weekend, and it was driving OK below 30mph but still making the noise above 30mph.  
• No lights on the dash, no warnings etc. 
• Above 30mph the car felt like it was juddering and when taking my foot off the brake (its automatic) the car was slowing down a lot more than it should be.
• Turns out the front right brake had ceased again (was extremely hot after the short drive) - so I had 4 new discs fitted, and pads all round, and replaced the front right calliper.  
• The noise was still evident - I thought if the brake calliper had been intermittently failing with unnoticeable signs, this may have stressed out the new wheel bearing I fitted in October.  
• Jacked the car up - no play in the wheel 
• Took the hub bolt out - no play in the wheel
• Took the wheel and calliper off - no play when trying to wobble the disk
• Took the wheel bearing hub assembly off (4 bolts at the back) and inspected the bearing, this identified a lot of play, and grease leaking out the seals.
• Changed the bearing again, and the noise has now completely gone 😃

I do have another problem now though, which I'm not sure whether it's due to the above or not - possibly!

There is a rattle coming from what I've investigated to be under the transmission bell housing.

The rattle is evident when idle, in neutral, in drive/reverse but only when the brake pedal is pressed (auto).  Once the brake is released and car starts moving, the rattle goes.  

I'd suspect this is the dual mass flywheel - I'm going to keep my diagnostic appointment on the 22nd and get it 100% confirmed.  

 

[RD1990]

Hi Jasonj,

I did give this a shake when I was under the car listening for the noise.  There was no play left and right (transversely) but there was play longitudinally (in and out the box).  I thought this to be normal.  
 

I checked for any other loose parts and couldn’t find any.  My next stage was to strip both under trays off to investigate but didn’t manage to get a chance to whilst I was under the car. 
 

Thanks,

Ryan