Zakster

This was my initial guess also, since the noise was pretty similar, but the shaft and the bearing are tight. Thanks for the suggestions anyway.

I think you are right Scotty. Seems the problem was actually two separate ones, bad rear tyres (the left one had a pretty significant flat spot, and both were probably too small as they were worn). I got the tyres sorted today, so when going straight things are a lot better, but something with the diffs is still a bit off: there's still the same resistance when driving at a low speed and turning sharply, seems to be worse when reversing. To me this feels exactly like a sticky diff. Strange thing: I tried reversing with full lock on the front wheels after a run on the highway, and the car reversed smoothly as butter, going both left and right. I tried turning the ignition off, re-started the engine and tried reversing again, and this time one of the diffs was clearly grabbing/sticking, same resistance again. The car is apparently equipped with an active rear diff as well - unless I was completely mistaken, there are tubes going into the rear diff. The car is now in a shop which specializes in diffs and auto boxes, so with a bit of luck this might be sorted with a fluid flush for both diffs, the transfer case and the ATTESA. Seems there might be some hope for the Old Stag after all.

Thanks for the suggestions guys. I noticed yesterday that the rumbling turns into much more violent shaking after driving a while, but I still can't figure out where exactly it is coming from. It seems to go away or at least lessen a lot when I back down on the throttle. Something clearly heats up. I also noticed that when reversing at a low speed after the problem had gotten worse, something seems so stick. There was quite clear friction, sort of in pulses, several times per one wheel rotation, maybe 3-6. I jacked the rear up yesterday, and tried rotating the tires just to get an overall impression of play. There is only little of it, maybe 1-1.5 centimeter on the tire outer edge before the prop shaft starts to rotate. Everything seemed to rotate smoothly as well, both sides, but I was only able to test this when the car had cooled down, testing when the problem is at its worst would probably be more useful. Wheel bearings seemed tight as well. The diff felt kindof stiff compared to my previous rear wheel driven cars, but still rotated without really having to force it. If I get the fluids checked, what else needs attention besides the front and rear diffs ? Engine oil and the ATF in the box are OK, the ATTESSA oil in the back is between min and max but looks pretty dark. I suppose the car's running in 4WD as far as I can tell, at least all the shafts are in place. I'm based in Wellington, NZ.

Hi all, I just bought a -97 Stagea RS4, and I think I might have made a terrible mistake: the car has two nasty problems I failed to notice before buying: A) very low frequency rumble/vibration when driving, which sounds like a really big subwoofer. I can't believe how I managed to miss that on the test drive. The road surfaces near the place I picked it up from were pretty rough, so general tyre noise might have masked it, or maybe I mistook it for tyre noise. I feel like a complete dumbass The noise is pretty much constant, but does get worse with speed. It's probably somewhere in the 10-20 hz region, and it's hard to pinpoint where it's coming from, at least when you're driving yourself. I can't make out a repeating pattern with it, but it's kinda hard to tell because of the frequency. It seemed to go away for a moment when I backed off the throttle at 100-110, but I haven't really had a chance to reproduce this behaviour, in lower speeds it is contant regardless of the throttle position, it was still there when I tried shifting to N. The engine is running fine, and the auto box shifts normally. There is a very light thud when shifting to D from N, which indicates some play, but it's not severe. Some slight vibration can be felt when driving, which no doubt is the source of the rumble. I crawled under the car and tried to shake and turn the rear prop shaft, but couldn't find any play in any direction. The car has done 190000 km so there surely should be some ? The rear diff wasn't hot after driving, only slightly warm to touch. ..and.. B) I noticed when doing about 100-110 that there was sort of "surging" from the drivetrain when running at an steady speed, even though I'm quite sure the engine ran completely normally. This went away when I started to accelerate slightly, and also if I backed up on the throttle. It felt like one end of the car was trying to run faster, and the other then caught up, and then it repeats and repeats until you either accelerate or slow down, this feels like pretty similar if someone was pumping the throttle slightly. Boost remains constant when this happens, as do revs. The rear tires are the same spec than the fronts, but are more worn, so could this difference in rolling diameter be a source of these problems, especially the latter ? The car apparently had an alignment 2 months ago, and there's no sideways vibration to the wheel. The ATTESSA oil level in the trunk seems to be full, but the fluid color is quite dark. I'll jack up the rear tomorrow and do some testing for play. I would really, really appreciate all the help and suggestions, this damn thing is driving me to ruin ,and I couldn't find anything on the forum. A very humble thank you in advance.