In other words, send the amp back for replacement and should be good to go?
That will not help, the issue will still be there.
That amp is a solid state amp and I could not find any information on its power supply. I hope that McIntosh would not do silly things... like use SMPS. If they did (use SMPS), get rid of the amplifier as fast as you can, and buy something else that uses a linear power supply.
The root cause is the magnetic coupling between the mains transformer inside the amp, and the crossover inductor coils (iron-cored, or one would hope -> air-cored) and/or speaker coils inside the speaker cabinet.
The solution is (much) better magnetic isolation - mu-metal iron sheets/ribbons, wrapped around the transformers inside that amp.
You can't change the above... so your only hope is to either:
- provide more space between the amp & speaker
- place a large mu-metal sheet barrier between the amp and speaker (very ugly.... unless you wrap it in leather or something and make it a decorative piece... that may work!)
- place the speaker crossover inside the mu-metal box.. that's inside the speaker.... but there are still speaker coils that you can't isolate from magnetic radiation...
So, more space is the solution... or get a different amplifier, but check the inside photos first to see if they isolated the transformers properly
The bottom line... both manufacturers failed miserably at isolating their products from magnetic interference... speakers (drivers) can be isolated too !!!