Rumble Sound-any guesses?

[1995Pathfinder]

I have owned a 1994 Q45a (converted to non-active about 2 years ago) for about 7 years and in the past 3 months or so I notice a low sounding rumble coming from the rear of the car at about 50 mph. Below and above that speed, the car runs quiet and rides nice. I assumed it had to do with the transmission so at 50 mph I shift into 3 and the sound is still there. So, I'm lead to believe that the transmission is not the source. Has anyone experienced this? I am reluctant to take it to the dealer because I always feel I will need to "sign away the 5th born". Car has 118,000 miles. Any help would be appreciated. Oh yeah, I also thought it had to do with the tires, but yesterday I replaced all 4 and the noise is still there. Thanks.

[1995Pathfinder]

After posting this message I just read the previous message some time back on a Q45 with the same problem. Sounds like it could be the driveshaft. Will check it out. Sorry for the double post.

[Q451990]

Could be a wheel bearing or differential as well.

Heath

[Q45tech]

Did you drain and change diff fluid every 2 years or 30k..........we change lots of differentials which get noisey after 120k from lack of maintenance.A new diff cost $2600 but most accept a $1000 junkyard takeout.

Wheel bearings usually last 180k or 10 years unless the car hit a curb.

[1995Pathfinder]

Yes. Had the dealer do the pressure flush at 100,000 miles and did not notice the sound then. Will check the driveshaft balancing using the Popular Mechanics article as a guide. Thanks,

[maxnix]

Had the dealer do the pressure flush at 100,000 miles and did not notice the sound then.

What is this? For the differential, all you need to do is drain and replace the fluid every 30K. At 100K, it is toast. Hope you're not counting on your brake fluid or coolan lasting that long. I won't ask about engine oil and filter, or refrigerant, lubrication and dryer.

[1995Pathfinder]

I misunderstood. I had the transmission power flushed at 100,000 miles along with the differential fluid changed. Oil and filter has been changed at 3,000 miles w/o fail since I bought it at 30,000 miles. BTW my shop manual gives no recommended "change" on the differential oil at all given the conditions I drive. Only to "inspect".

[Q45tech]

Inspect means to test it, not just look at the dirty fluid and top it off as dealers do.

You have to understand there is little profit in changing fluids compared to replacing a hard expensive part...........since the dealer markup is close to 100% on parts.$5 on $10 worth even $20 on $40 worth doesn't help the bottom line much.

Just like transmission flushing.........it takes 25 flushes to equal the gross on a single transmission change and the 25 flushes take 5 times longer than the real time on a transmission swap.

[PalmerWMD]

Could be a wheel bearing or differential as well.

Heath

I'm with Heath on that one.

Fred...