This is the second time I post something about this.

My concern is basically about audio levels for certain music albums (a lot actually), from a lot of rock bands (Metallica, Foo Fighters, Meshuggah and the list keeps going) or even in Hip Hop albums is lower than competing services on same settings. 320kbps
Only happens on Android
I've been using Deezer, Google Play Music All Access and Tidal in the last 3 months and I just came back to Spotify and the difference is very very noticeable. When I switched to Deezer I noticed it and I was able to test both services at the same time (free premium time, I think it's 15 days for the trial period and I still had a couple of days of subscription on Spotify). The test is easy to replicate, get the same song (use Wasting Light - Foo Fighters as reference), same speaker/headphone configuration and set the volume to a comfortable level on any service and hit play on it, then switch to other service with music still playing and hit play again (it automatically stops the other playback) listen to the same spot and do it over and over.
After the 2 week period I got accustomed to the level and switched to Google's all access and didn't notice and difference repeating the same test only this time was Deezer/all access. Then after a month I joined the trial for Tidal and did the same and no difference in audio levels.
Now I came back to Spotify as premium user (always been premium) and the difference is noticeable and also frustrating.
It's worth noting that I did the same thing on iOS (my brother has an iPhone) and couldn't get the same results. I also did it on PC and Mac and got nothing, but I tested other 2 Android devices and got the same results as with my personal phone.

The reason I keep coming back to Spotify is because I think it's the beat overall service.

I hope someone important reads this!

Thank you very much for reading this long post.