Knocking noise

[RickHaleParker]

A hollow, muffled, like somebody is drumming?
Sort of like the sound a large diesel engine makes?

[cass3958]

Finally go to the bottom of this noise this week.
I had taken the car back to the gearbox garage but they assured me the noise was not from the gearbox. Took the car back to the cam belt garage and they assured me it was not coming from the engine or the cambelt area.
So I finally got the car up on a jack and removed the front right wheel. Checked for any scrapping marks but none. Fiddled with the drive shaft and could not feel any play. Checked all the nuts and bolts on the suspension and brakes but nothing loose. Frustratingly put the wheel back on and felt a small amount of sideways movement in the wheel so got underneath. I found some movement in the lower ball joint which should have been picked up on the MOT I had done on the car in December. Bought a new ball joint and fitted it last weekend and the noise has now gone. I can only imagine there is an imbalance in the front wheel as I also noted that the wheel balancing weights had come off the inside of the wheel, this imbalance is affecting the lower ball joint making it move more than normal and a little bit of wear is causing it to knock or tick when cold. Time to get the front wheels rebalanced I think. Anyway I only surmise but replacing the bottom ball joint has got rid of the ticking noise. Harrah.

[seggs]

I was following these posts because I also had a fairly severe knocking noise from my xc90 2.5t with 125k. My noise was worst at startup and got better as the car warmed. It made the most racket under load, and none when idling. I was worried about the oil flow to the valve train, but after some work with a stethoscope, decided that wasn’t it. Then i turned my attention to the accessories driven by the serpentine belt. I was concerned it was the alternator, ac compressor, or power steering pump. After pulling the belt, the tensioner pulley had slight play in it. After replacing it, problem solved!
I always tell others to investigate the simplest stuff first, and not to jump to the worst case scenario until other things are ruled out, but it seems I also need to be reminded. At 125k, I could have easily justified in my mind how more expensive repairs may be needed, and started throwing money at a problem that was simple and cheap. Hope this helps someone else to resist thinking the worst, and instead follow the clues.