When listening Christmas songs on my 12.9 inch iPad (2018), I noticed that, once the volume is turned up to 3/4 of max (or higher), a strange buzz/resonance (hard to describe) "appears" in the background of the music. It's not just 1 speaker, but all 4 producing the same buzz/resonance. The 2 on top are a bit louder though. Can someone please check? Just want to make sure I don't have an issue with my iPad. Using Tidal (320kbit rate) and really noticed when playing the "Christmas Canon (Cannon in D)" song. Other songs produce the same, but the above song was a great test subject. Thanks!