No not noticed this, perhaps re-tune the speakers to their location, try the different orientations of the ‘pair’ and maybe adjust EQ settings until you (hopefully) find the best sound to suit your environment/own ‘taste’.

Would love to have Amir test one.  Send him one of yours! ;)

The IKEA/Sonos picture frame measured pretty well.

Wow! What is an upper mid treble and how does one distinguish it from a lower mid treble? Or indeed from an upper treble mid?

How can I explain in language you might understand? Using those flappy things on the sides of your head. 

By the way, we don’t share a vocabulary that adequately describes an aural experience. If I asked you to describe a cricket so that I might recognize one if I see it, this is not impossibly hard, but it is much more difficult to describe the sound made by a cricket.

Anyway, there might be an acoustic property of the room that is unfortunate. It is interesting that drum impacts trigger your issue. It is a property of solid matter that, when subjected to an energy “impulse” (like a drum hit), the object will respond with its natural resonant frequency. We’ve all played with this as kids when we pinged the glasses and such. That drum hit might excite a nearby object. When I installed SUB with my PLAYBAR, I had some nasty resonances in the windows. Bass thumps would cause window rattles. An observer might have thought I had gone mad as I walked around the room thumping the walls  near windows with my fist. The windows would reply with their resonant frequency and I could subdue this by inserting small cardboard shims. After I completed my thumping walk, the windows were silent when the chase scene thumped.

You should also experiment with the FIVE’s oriented vertically.

Hi Buzz. Thank you for your thoughts. I'm fairly sure the sound I am hearing is coming directly from the speakers. I'll try running Trueplay again and see if there's is any change. The speakers are vertical. Am I right in thinking that it only in that orientation that the Fives play in stereo? 
I hear you about the unwanted interactions with the room though. I have a cat flap in the room where I have a Sub and Playbar that was driving me nuts until I identified it and stopped it rattling! 
Thanks again for your interest. 

I have the same setup and have used both vertical and horizontal I prefer horizontal as it gives a wider soundstage 

Whichever you choose both are stereo 

There is a tweeter near each end of the long axis of a FIVE. A single FIVE is stereo in the horizontal orientation, but you need to almost press your nose against it in order to achieve a significant sense of ‘left’ and ‘right’. In vertical mode a single FIVE is mono. A bonded pair of FIVES have a left and right speaker, but in horizontal mode the inner tweeters are subdued. Some feel this scheme results in a better sound stage, other listeners do not.