For me it is quite obvious it is an artifact. This is noise produced as an artifact from something within the chain. Or how do you explain the exact same noise is produced thru the whole album which is 15 hours ? Perpetual
is only 8 hours, not 15. Are you detecting the same problem in Somnium
too, which is also included in the Blu-Ray release (leading to the 15 hour total)? If it is in both--and not in the original Somnium
release--it could be an error.
For what it is worth, I can't hear the noise artifact you're referencing, but my ears are not as good as those of others here. There is a funny sound that comes and goes from about 30 mins in to 65 mins into Perpetual
--almost like compressed air that is being released at an unsteady rate. I assume this is what Altus is detecting too. I assumed it was intentional, but perhaps not. I can't hear it on my bedroom speakers; I can only hear it with headphones or on my stereo.