I recently took my 2004 x-type on a long road trip, and ingeneral it performed flawlessly.Butafter many highway miles at 65-75 mph the typical driveline whine started toget annoying.It sounds like a gearwhine noise or maybe the driveshaft being slightly out of balance, and makeswhat seems like a “resonance” type of sound at specific car speeds.The rpm has no effect.It’s a higher pitch sound than you wouldtypically get from a worn bearing, and sometimes there are several sounds thatseem to interfere and give an oscillating effect with a frequency of about 1cps.It’s almost like a symphony ofsounds from various mechanical components.At speeds below 60 mph there are no noticeable sounds of this type.
I read about one TSB, XT100-11, “Driveline Noise – SoundTransfer From Transmission and Driveline – Install Sound Deadening Liner”.I references part C2S 40533 for theliner.I know it’s been a long timesince the TSB came out, but is it possible that the part is still available? Ifnot, is there a substitute, or are there other methods to reduce sound transferfrom the transmission/driveline to the cabin?

 

sawduster, from what you are describing, it is sounding like the carrier bearing is making a little bit of noise. You can try taking a needle attachment on a grease gun and push some grease into the bearing. If your noise changes/goes away, then you know the carrier bearing is the source of your noise.

 

Thermo, thanks for the tip. I considered this before but never followed through. I will give it a try and report back on my results.

 

Well I added some grease to the propshaft bearing, but there is no change in the noise I am hearing. To be clear, the noise mainly starts at 65 mph, has a relatively high pitch. It does not correlate with engine rpm at all. If I let up on the gas at 65 mph it immediately abates somewhat even though the speed is the same. The pitch is about 620 Hz (for referenced the dial tone on a phone is 440 Hz). Also, 620 Hz is 37,200 cycles per min or rpm in a rotating machine.
I also tried taking it up to 65 mph and then shifting into neutral. There was no change at all in the noise. So I suspect it is not transmission related or, given the frequency, not the transfer case. I'm thinking it's something in the running gear, but usually a wheel bearing would make a sound that increases pitch with speed. Anyone have any ideas?

 

It sounds like differential whine to me. My GTO and previous S-Type did that. Was loudest around that speed and sound lessened slightly off throttle.

 

Torrid,
Thanks for the tip. I found a video on youtube that duplicates my noise exactly and also suggests the rear differential:
My only question is that it doesn't sound like it's coming from the back end, but I suppose it could be deceptive.

 

It is an AWD car. I'm not sure how complex the system is, but you basically have three diffs. The front, rear, and a center transfer case to split the power front/rear. I'd start by changing the fluid in each.