Checking last night I also got it on Amazon Unlimited. First 2-3 songs play at set volume then next one play’s at reduced volume and then next songs go back to set volume.
I suspect this is due to differences in dynamic range compression in the original recording used to master the product..
If you compare a wide dynamic range recording with a compressed one, then the higher dynamic range recording will have a much lower average level. If you think about it this is obvious otherwise the higher dynamic range recording would cause clipping.
So the only way a streaming service could avoid this would be to compress all recordings to the same average level. I suspect some do, but this is probably not what you want.
This problem you are experiencing is due to the lamentable technical standards and expertise in the pop recording industry.
The only device that would solve it would be a gated compressor. This would compress everything to the same level and keep the average playback level constant.
I doubt this is what you want, as I suspect it is the quieter ones that are the better recordings technically with better dynamic range.
