Well, As far as the calling part is concerned, I'm not too sure. But yes, there is definitely poor audio from stock music (Google Music) App via 3.5mm headphone jack. It's not just the Nokia 6.1Plus with this issue. Even Zenfone Max Pro M1 (4GB) also had the same problem. If you plug~unplug the 3.5mm audio pin in the jack few times, the Buzz might go. Pretty strange actually.
Now coming back to lower output level, I've tried listening to some Pink Floyd songs on a busy day while I'm traveling in train. I literally had Hard times and mostly frustrated. When I played the same songs using 3rd Party Apps like PowerAmp or Gom Audio, Boy I was in for a treat. They just make you forget about your complaint.
But what if you're subscribed to Google Play Music and paying every month and have this low output issue in the app???? The EQ in Google Music app is good for nothing. If you try to adjust the settings, it further drops the level making you realize that Bypassing the EQ gives you maximum output the app can support which is technically the highlight of the topic here.
Also I need to mention that I use Jays A JAys Five earphones and Beyer Dynamics Byron Wired earphones. "So not the crappy ones"
But haven't found the reason why the Stock Android like phones (Asus Zenfone MAx Pro M1 and Nokia 6.1Plus) has Low Audio output from Google Play Music App????
Here's something I would like to share and I hope you're supposed "Buzzing Headphone concern" might get some light. Few points to be noted....
1). I recorded few tracks from 2 devices. a) Zenfone MAx Pro M1. b) Redmi 3S Prime.
2). Now both the phones were recorded via 3.5mm headphone jack thru my M-Audio sound card on Cubase7 Digital Audio Workstation.
3). THe EQ in both the phones were bypassed.
4). Google Music App has been used to record the Audio samples.
5). Here's the link.
These audio samples were made to bring into notice of Asus how the sound is poor in Zenfone MAx Pro M1. You can here a similar Buzz in Zenfone MAx Pro M1 audio samples that you hear in Nokia 6.1plus phones and also the Audio level is significantly low as well. Redmi 3S Prime had no issues with Audio.
Is it something that Google providing Stock Android features to companies like Nokia or Asus giving certain recommendations or guidelines for the software to operate in the device though the phones are fully capable of producing the best Audio Experience. Courtesy of 3rd party apps like Gom Audio and Poweramp that literally overrides the system EQ.
The only query that matters now is If the Low Audio issue is a Software problem or a Hardware problem????
I don't think It is Hardware problem bcoz apps like Gom Audio and Poweramp works perfectly well with louder audio levels.
I'm mostly keen that it is a Software related issue Some Bug maybe and If the developers provide a proper update, this problem can be sorted out once and for all.