I think the term "unusual" can be addressed from 2 different perspectives. There are those who use a wide dynamic range intentionally and with skill for "dramatic" intent, and there are those who end up with a wide dynamic range due to to lack of knowledge on how to mix/master properly, or accepting flukes / mistakes in volume spikes or dropouts. Mania certainly falls into the former category. I'd say many fall into the latter category, which still often has a charming, and in some cases, powerful effect.
That said, I think we're conditioned through how pop/rock music is mastered and consumed (boombox, in car, headphones, cellphone speakers, etc.) to expect to hear everything at about the same volume all the time, so I love it when noise artists take advantage of the richness of potential of volume variance, which is totally limited in most other music. There is no reason not to have quiet parts be actually quieter and loud parts be actually louder on a recording designed to be listen to on a decent soundsystem in a room, where the sound of the tires on the road aren't going to drown out what is going on down below, for example.
This issue of range also applies to the range of dynamics within a small fraction of a second of audio, and not just between "parts" or passages ca. 1 second or more long. On a lot of GREAT and the loudest sounding recordings, the waveform it totally brickwalled so you basically just have one volume all the time, and the noise just sound loud as fuck. Cool when done right. Still, I appreciate those that take it back a little bit and allow the jags, peaks and valleys to really differentiate from each other and the noise to really RIP. Might require turning the overall volume up a bit. Again I think Mania falls into this category, though I've never looked at the waveforms of one of his recordings.
The tape format works wonders for many artists whose recordings are unmastered - take a digital recording with some awkward volume variances and dub it to tape a little bit in the red, and the dynamic range is tightened up nicely. This can of course be undesirable for certain recordings where a wide dynamic range has been intentionally achieved. This is where I think CDs are great, but I really only want to hear CDs from artists who know how to mix / master their music tastefully and somewhat precisely
Some recordings off the top of my head that make use of a wide dynamic range:
KIRAN ARORA - Formication - a new masterpiece - roaring jags of noise with pressure and intensity, bug-like clicks cutting through the mix perfectly, passages that volume, parts that blast even louder than you were expecting.
TAINT - Sex Sick - insane disturbing jumps in volume between all of the disgusting samples and the piercing sadistic feedback that blasts in over and over again.
SEWER ELECTION - Sex/Death - the beginnings of "Sex" has such a dramatic jump in volume in the fist few seconds, that almost feels off, but that is what makes it so great. Yes, this is NOISE music, why shouldn't it rip your head off?
THE RITA - The Voyage Of The Decima Mas - Example of a brickwalled waveform (from my memory when I looked at it one time) that's basically always either one volume or silent, but gives an incredible audio illusion of wide dynamic range with all the airy/watery parts.