Without being there to see it,

But... Speaing as a guy who has made his LIVING fixing electronics since 1981, I'd say it sounds like you are hearing the "Switching Transients" of the charging adapter's Dc-to-Dc converter.

It may be that charging during use is just not going to work. If you had a charger with a "linear" type voltage regulator, you would not have this noise - problem is, linear type regulators are larger and generate a lot of heat internally, causing failures of the components. This is why the "switching regulator" is so popular. The disadvantage is that switching regulators are noisy - as you have observed.

So, I told you what the problem likely is, but can't come up with a solution. If it was me, I'd build a linear regulated charger with a fan in it... but then, electronics is my career and hobby!!

The only thing I can think of is to stop the noise at the source - the charger. Again, you can only do this by not charging during use OR by substituting a non-switching charger. But again, no one makes such a charger!

So there you have it, a complete answer - that does you no real good!
(During the week, this would have cost you $65).