Sounds like your pinion is pointing down since you cut the springs and lowereed the car. I would suggest that when you accelerate the vehicle the pinion rotates up enough to lessen the noise and also the same goes for when you apply the brakes, the pinion rotates upward to the point where the driveshaft angles are acceptable. IPD sells a set of adjustable control arms that I just so happen to use on my V8 conversion to adjust the pinion angle and I can tell you that they are the way to go to get your pinion angle where it needs to be to be quiet again. I can't guarantee that I have explained your problem, but at any rate, good luck.

I agree with Stickbuilder that your (now) offset rear end could well be a factor. But I don't think the situation is as dire as he suggests. My '80gle V8 (IPD lowering springs and rear offset left about an inch), gave me over 100,000 fun miles on it with no undue noises, pinion/u-joint problems, etc.

But I think "Center driveshaft bearing seems OK." isn't good enough. I would give it a good physical, and the rear u-joint too—since both ends of the rear shaft may be feeling some effect of the offset rear end. Maybe I was just lucky.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Sounds like you have answered your own question. You stated that you had cut your coil springs by 1 1/2 coils. You may have changed the pinion angle to the point to where you are causing it to bind when the car is on it's wheels. When you unload the suspension, you relieve the situation. Try putting on a stock set of springs, and see if the problem does not go away. You may need to build a set of upper control arms that are adjustable to keep the pinion angle as it should be with the lowered springs. It's a lot of work, but if you want it in the weeds, that's the way to go. I do this operation when building a street rod, and included angles are a way of life. The drive shaft (and yours has a split shaft) needs to run at a preset angle to remain quiet. You may even be generating the noise from the center bearing too. Did you cut the spring at the Progressive wound end or the other end? The ideal thing is to buy aftermarket springs, so that you don't lose the progressiveness of the spring rates. Like my old Pappy used to say.....When you change it from stock standard, there will be problems.

Bill

Are you sure it's the rear diff? Weird for those to have problems. On the other hand, I've had parking brake shoes come apart and make all sorts of unusual scraping noise from the rear. I know you said your brakes were A-1, but have you checked the parking brake shoes?
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'92 240 wagon, 270k, '88 240 sedan 281k

Sounds like the pinion bearings,does it start making noise after a set speed, say 40mph on up.The one thing to check is to see if the pinion seal is leaking and if you can move the yoke from side to side are in and out,any play and it's bad,I would start with the pinion and go from there,anyway you look at this you have to take it apart.
Rodney