V6 XWD rumble

[PeterV]

My tow car, 2009 spec 58 reg 2.8 V6 XWD has developed a front end rumble at 40mph. Power on, over run or coasting strong sound of road noise but no vibrations. Tyres were low on tread so have been changed but no change. Full major service recently new shocks fitted at the rear during service but fronts given clean bill of health and are still solid with no leaks. No steering wheel wobble. No wheel or joint movement on jacks. So questions or possibilities please coz this is just weird!

[Max Headroom]

Hmmm a 'rumble'? I think I would be pointing the finger at a wheel bearing if it was mine

[sgould]

Does the noise change if you go round left and right bends?

[PeterV]

Nope there is no denote as you take turns. Constant sound even under heavy break turn in. Wheel bearing was my first thought, but the evidence both physical and melodic just don't fit ? My 13 year old has better hearing and says it be loud at 40-45 mph still audible at 55 but only just. Gone below and above that narrow window. Will do some stripped down checks tomoz coz this is just way to puzzling. Maybe a bit of front to back wheel swaps coz I've been caught with sound transfer before.

[smurkenstein]

I don't think you mentioned. Is the sound constant pitch or speed dependent?

[Petemate]

Given that it is there, power on or off, and coasting, and speed related, it must be something from the diff through to the wheels IMHO. Diff bearings? Drive shaft support bearing, if there is one?
Pete

[PeterV]

Will be diving underneath today to see if there are any drive shaft bearings. Kinda wish I could figure out which side it"s coming from but we can't. Even with the kids ears leaning all over the show its hard to tell. And if he tries any harder we will probably get arrested 

[sgould]

I wider if it's tyre scalloping?  Like the 9-5 gets.  Uneven wear on the inside edge of the tyre.


On the 9-5, it's odd.  The wear is on the rear tyres, but the noise appears to come fom the front.  If your car is used a lot for towing, the rear weight may have splayed the tyres and worn the inner edge.

Again, on the 9-5, the noise is loud at lower speeds and disappears at speed.

[Audax]

I've known the rear banana arms on the 9-3 to cause noise like the 9-5 gets when they get worn out but to be honest I've never seen underneath an XWD and have no experience of them so don't think I can really help. One thing to check would be all suspension is in a good state as if you have a blown shock/broken spring then the diffs might be sitting differently and causing a noise. If the fault is in the XWD then you'll need to find someone who understands it.

[PeterV]

I must admit the noise is very "road noise" like so tyres seemed the way to go to start with. Hence the change of well worn fronts.
Rear shock blown.....Rear tyre.... Noise transfer to the front?? Think I'll do the tyre front to back swap and see what happens. Bloody wet out there and the sports cars hogging the garage in prep state for Mondays show.

Things always arrive together. Just had to changed the exhaust centre section of the 93 coupé. Damn clamshell clamp bolts rounded on one end. Grrrrrr.... What next he sighs 

[Audax]

It's the case that as many tyres get worn they get noisier, it's a 2 minute job to go and check depths on the rears and run your hand around them. You will feel the ridges if they have gone out of shape or worn unevenly, they'll feel smooth in one direction and stepped the other if this is the case. What tyres do you have on the back of the car?

[PeterV]

Just a quick update. Measured rear tyres. Offside 8mm all the way across. Nearside (damaged shock side) 8mm outer edge 4mm inside edge. Looks like a good clue here  PS Pirelli rears Continental fronts.

[PeterV]

OK solved that then. Well more "identified that then" than solved. Front to back wheel swap moved sound to front nearside rather than seemingly both front sides. Sound is now there 30MPH through 60MPH. Sound is much louder but quieter on rough worn out road surface (of which there are plenty around here).
So on goes a full set of 17" wheels. Sound gone but yikes so has the handling. Very washy feel on these rims with horrible turn in  (cambers messed up I guess). Surprising this coz the 900, GM93 and 95 never seemed to worry to much about wheel size changes.
Back to the 18" as they were then and wait for:
a) things to settle (Unlikely)
b) tyres to wear out
c) get annoyed enough with noise to spend another £300 on a pair of new boots

Large towel and Scotch please..... horrible smegin weather out there 

Cheers all, would not have thought of this solution for a long long while with out ya 

[Audax]

Get the alignment checked out would be my suggestion before spending any money on tyres!

[PeterV]

Front to back alignment laser checked, all good. Front & rear camber and toe checked, all on spec. Well +/- my workshop floor which is pretty good and certainly good enough to set my sports car. Did use to level the sports car on floor tiles and sand but found it wasn't really worth it.
So good news I don't see any issues here 
Only trouble is moving the sports car out into this weather means a busy day tomoz re-preping it for the show on Monday. Ho hum never mind