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I have a Ford Focus 2004 1.6l that has done quite high mileage 155k.

It had a problem wheel bearing on the front right (drivers side) which was replaced along with a full service and some other bits. After this it was silent and driving fine for about 1k miles.

Over the last couple of days it has developed a noise from the rear of the car which appears to be getting louder. It sounds like driving on a flat however I checked the type pressure yesterday and it was fine.

My suspicions is that it is either a wheel bearing on a back wheel or a problem with the exhaust.

The strange thing is that it is loudest from 0-25mph after this it actually gets quieter. Then from 40+mph it seems to come and go but never as loud as it is at around 20mph. This to me doesn't fit with a wheel bearing that tend to get louder and louder with speed from my experience on the front wheel.

How could I try to diagnose this more before getting it to a mechanic?

I really need to narrow it down a bit more to know if its safe to drive as I do around 40 miles round trip a day for work.

Thanks!

  • Driving on a flat = repetitive slapping sound? The volume of the sound peaks at 20 mph? Is there any change in pitch? Or is it just an intermittent transient noise? Does it get faster with speed or stay constant? – Bob Cross Feb 25 '15 at 18:44
  • Hey Bob, yeah that is a good description, how I described it to my mechanic over the phone was like having trainers in a washing machine! I think it peaks at about 25mph and at first I thought it got quieter past this speed but now I actually think it stays the same volume but because the engine and other part get louder it just gets drowned out. Today it has got a lot louder though, got to about 40mph and it sounded like a plane taking off. It's due to go in to the mechanics on Saturday. – Charles Feb 26 '15 at 8:41
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The standard test for a wheel bearing goes something like this:

  1. Jack up the appropriate end/corner of the car and support it on axle-stands
  2. Grasp the wheel firmly at top and bottom and try to shake it - there should be a tiny amount of movement, any more is suspect.
  3. Repeat step 2 for side-to-side
  4. Spin the wheel and listen for any unusual noise, or resistance
  5. While you're at it, check the brake pads for wear...

Another thing to check is to see if either rear wheel feels hot to the touch after a run - use the back of your hand, carefully...

While the back of the car is up on stands, a visual check of the exhaust should reveal any obvious problems (e.g. a failing mount rubber) - make sure you do this with the engine cold, as exhausts can get very hot. Also check for anything else loose - mudflaps, stone-shields, etc.

A slight exhaust blow wouldn't make the sound you're describing - they tend to sound more raspy, a bit like the big exhausts that boy racers fit to their cars...

  • Great answer Nick, I brought a Jack on the way home yesterday and the back right wheel is really knocking when spun by hand. My mechanic has ordered a wheel bearing on my diagnosis so hopefully its right :) – Charles Feb 27 '15 at 8:33

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