Axle Ping. Yeah, it is a Thing. Here are some potential solutions.

Axle “Ping” is a phrase used to describe a variety of noises that can occur from the front of 1999 and newer Volvos.   

Volvo issued many service bulletins focused on odd noises occurring on P2 XC90 (2003-2014) models, but these same issues can occur on any Volvo with CV joints (FWD/AWD.)  It appears to be most common on XC90, S60R and V70R models. 

The word Ping doesn’t really describe the sounds produced by this issue and may actually be a poor translation from the original Swedish technical bulletins.

The sound tends to be more of a knock, clank or clunk sound but the sound can potentially echo down the axles some situations and make a more ringing harmonic sound, hence the "ping" moniker.

Axle ping is most apparent when you shift the car from reverse to drive and back again with your foot on the brake.  There will be a noticeable clank noise upon the shift in directional load against the drive train.  This is easier to produce on automatic models but the same applies to manual transmission models. 

This same noise can occur while cruising when you are on and off the throttle.  It is most noticeable at lower speeds.

Some cars may only experience the noise when accelerating hard or engine braking (manual trans models.)

It just sounds like something is loose in the drive train or suspension but rarely is there an actual noticeable sensation from it (i.e. a feeling in the steering.)  It’s mostly just noise.

So what causes this noise? It seems to be caused by a small amount of play in the splines between the axles and the wheel hubs. This play allows the axle to shift slightly in the hub.  It’s usually a very small amount of play but it can make a lot of noise. In some cases, the axle and/or the hub have actually worn substantially and nothing but replacement of the worn components will make the noise go away.

At one point Volvo created an “anti-ping” bolt that turned out to be an odd but very effective solution. It was the same stock axle bolt but with a steel spacer that had a rubber cone vulcanized around it. Volvo has since discontinued this part for the earlier models (the later bolt is much shorter and not compatible.) We theorize that they did this simply because the cars that used it reached the end of their warranty term so the ping noise it isn’t their problem any longer. We could be wrong about that but the timing does seems about right. 

How do I solve this annoyance or determine if the noise I am hearing is axle ping?

Volvo uses "torque to yield" axle bolts-  They permanently deformed during the torqueing process, so they are considered one-time-use fasteners. Re-use at your own risk.

Proper Axle Bolt Installation

• Loosen up your wheel bolts.
• Jack or lift up the car and remove the wheels.
• Remove the axle bolts.
• Push the axle as far inward as it will go. This sometimes requires tapping on it with a hammer.  We recommend using the axle bolt for this since it is very long and should be replaced anyway.  You shouldn't be able to completely back the axle out of the hub but you should be able to expose a significant portion of the axle splines.
• Apply some anti-seize compound or CV grease to the exposed axle and hub splines on the axle itself and the inside of the wheel hub. 
• Push the axle back in to the hub and install new bolts but don’t make them tight yet.  Just make them snug so the axle is pulled back in to the hub.
• Remove the center caps from your wheels and put the wheels back on the car.  Tighten the wheel bolts until snug then lower the car.
• Once the car is back on the ground, torque your wheel bolts to 85 ft lbs.  
• The axle bolts are angle torqued (stretched) and should be replaced with each use (although we typically only do so after a few uses.)
  • Front axle bolts: Torque the front axle bolts to 35 Nm (25 ft lbs) then turn them another 90 degrees. (this is called angle torqueing.)
  • Rear axle bolts: Torque to 50 Nm (36 ft lbs.)
  • We find that most cars have the bolts zipped on with an air tool which doesn't correctly tighten them since they are torque to yield bolts
• Put your center caps back on your wheels.

At this point, the noise should be gone unless your axle and hub splines are very worn or you have a different issue.

The noise may come back after a while but absence of the noise after this procedure will help you determine if the noise is axle ping or something more concerning like a problem with your differential or angle gear.  It is very common for AWD models to have a worn out sleeve coupler between the transmission and the angle gear which can cause some odd noises that are difficult to diagnose. That issue is most common with AW50/55 transmissions. 

We've heard of people using thread-locker or other more permanent methods to deal with this issue but what are you going to do when you need to disassemble the suspension to replace other parts?  It won't be easy if the axle won't slide out of the wheel bearing hub.