Anyone else have a problem with distortion ... not particularly on loud passages

I'm becoming more certain it's on the DSP side of things , not the actual speakers ....

I can be listening to Piano music say (via the phone, which is via the USB) and get a slight background distortion at times (as said , not on particularly loud passages), seems to be centre and at least the drivers side.
It kinda drives you mad, like Glenn Gould drives you mad with his humming.... in fact it's quite like that in the way it follows the music.

I've yet to try it via the analogue audio in ... (i.e. 3.5mm to 3.5mm)

I've seen similar to this on automotive Class D amps before now , at least I've still got some warranty remaining to get it sorted whatever it turns out to be ... software or some part of the hardware chain.

Anyone else ?