I wonder if all 552 chassis ring? And quite a lot in my case. The 552PS doesn’t. My NDX2 doesn’t. My 300DR and PS doesn’t. If I stop music I can for a second or two hear it ziiiiiing. I believe I had another naim box that did this but not as much. It must colorise played music if it sings along to music like this? Maybe added reverb is what makes it sound so great 
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The 552 is on metal feet…so are the feet all making contact?
It sits on a Fraim Lite shelf so yes 
So long as it’s sitting level and all the transit bolts are out and the suspension duly released, I’ve never heard of a 552 head unit ringing.
Is some form of vibration being introduced in to the Fraim-Lite stack?
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My olives can ring after loud music, from memory my SC, 135’s have a plastic slide on the back of the case that can be move one way or the other to tune the box ring. If you tap the top of the box with your finger you can tune them to the same tone by ear if you like. Back in the day some would put an ice hooky puk on the box to stop the ringing. Anyway not sure about 500 systems ( very much doubt they have plastic slides.
The 552 i think has an internal large brass bass supported by springs, so very little vibrations get through to sensitive electronics, id also imagine it’s probably tuned too.
Owning mana acoustic racks witch can also ing after a good loud session.
Hope that helps a wee bit.
Yes it does, my 552 on Fraim did ring… until I put 3 hockey pucks on top… no more ring.
Try it
Yes, it should ring. Note that the circuitry on the suspended mass loaded boards is unaffected, and it seems to sound best this way. Damping the ringing sounds worse for some reason.
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I second what Rooster has said above. The 135s have a couple of black plastic ‘clips’ (not sure what to call them) at the top rear of the ‘tray’ holding all the electronics inside the case. These can be slid along the tray to whatever position is best to control any resonance.
(This explanation sounds rather odd, but look at the back of the amp and all should become clear.)
Thank you Richard, very interesting… I will take it out and have a listen again. I couldn’t hear much difference when I put them on
I tried a hockey puck on the case when it was suggested many years back by CK. I preferred without. I guess it was a bit like the old damping strips on Olive kit - generally preferred without them engaged, or even removed all together.
What is absolutely critical though (and has been mentioned here above) is that all four feet of the NAC522 are absolutely square on whatever surface it’s sat upon. Few surfaces are ever completely flat - not even glass. Even the tiniest bit of play in any foot will impair performance. It’s worth having some of the special wafer thin shims standing by.
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Thanks Richard. I can add that I do have my speakers rather close to my 552 and that it’s some tones that make it sing. If I go up close and talk to it (we all do?) then you can easily trigger it to sing too. And even though I put a vinyl record weight on it it still sings but lower amplitude. Anyway, if they all act like this but more or less given room, distance from speaker etc then it is what it is. I mainly want to know it ia ok It does sound beautiful.
All the feet touching. That is related to something else I guess like feet connected to suspension or? I have it on a fraim lite and I can not feel it wobble so guess it’s ok. I’ve read placement on the frame is critical too but seems related to frame with glass shelves in that 552 should be placed at the very front to minimise resonance.
Yes, all four feet need to be firmly connected to whatever surface its sat upon in order for the suspension system (and, I would imagine also the “quiet room” functioning of the outer case) to work properly.
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Is the Fraim sited over floorboards and/or a floating floor (e.g. wood over concrete)?
When I had my LP12 on full Fraim, it would wobble very slightly when walking by – a prompt to get it on a wall-shelf.
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Oak laminate floor on mdf and does not move. 552 on top shelf (4th level).
Perhaps do the half-full glass of water test **on the top shelf of the Fraim – very, very carefully of course!!!
** in absence of having a vibrometer.
A couple of quick stomps nearby should reveal if you have any low frequency bounce.
Hmm I moved it so the feet are more close to the front and the ringing dramatically got lower. Maybe my fraim lite shelf is not perfectly flat.
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On my Fraim Lite, I have all the boxes positioned with the front of the Fraim.
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There are many aspects in this respect of the Naim design that affect the sound as far as I know. The same with bolting down the toroidal transformers. I suppose this should also require proper placement so that the equipment does not ring along with the listening experience. Particularly noticeable when I’m listening to ring along with Max Bygraves. I can see the head units being sensitive to microphonics but a bit surprised with the separate power supplies.
Yes i should be as close to the front as possible and the 552 sound much better with Fraim glass .
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I have too in that the front of the boxes align with the edges on the Fraim. But it seems like in my case that if I push 552 even further so the feet are closer to the edge and the front sticks out 1cm it rings much less 
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