I have a Rossini Apex player and Clock with a Naim NAC 552DR and NAP 500DR into Sonus Faber Guarneri Traditions.
With the volume on the pre-amplifier turned up to maximum, there is both a quiet hiss and lower frequency hum/buzz audible with my ear up to 1-2 feet from the speaker on both channels. Is this ‘normal’, and if not should I let it concern me?
Hiss, yes, but when my ear is as close as 3-4 inches to tweeter. Low frequency humm, no. My setup has a passive preamp with Karan Acoustics’ KAS400 power amplifier.
Sounds like you are suffering from Audiophilia Nervosa 
.
No systems are specified to have 100% attenuation of noise and you are effectively speaking of using a 140 watt per channel power amp into speakers of average sensitivity ( 87dB quoted) FLAT OUT. With those figures you are going to hear something.
Reset the volume control to a realistic listening level. Hear anything without any music playing ? Only if you now can should you be concerned. You may have a little 50/60Hz hum which you could spend hours chasing down ( even if you could reduce it) but if it is inaudible with the equipment used normally I would not worry.
One aspect that isn’t covered however is the line level output you have chosen for your Rossini. Please ensure that an appropriate one is chosen. Start at 2V with Rossini set at 0.0dBfs and only change if the preamp volume control needs to be used at a very low or very high rotation ( it should be roughly somewhere between 9:00 and 3:00 o’clock for an average suitable listening level).
Thats the naim gear renowned for it, and quite a few posts over the years on the naim forum about it.
I had the same 552dr and 500dr into a rossini/clock, and it was never quite out off the speakers, especially if you turned the volume up. But since i swapped them both out, my system is dead quite even at max volume, no hiss what so ever, and especially no hum.
If you are using naim cables as well, non off these are shielded, and so pick up all sorts of noise, and can cause hum.
What he said
(Coming from another 552/500 owner)
(the buzz is from the 552/500 power supplies)
Thanks. I know there is noise directly from the power supplies (barely audible in my case although was louder from my CD555 PSDR before I traded it). Is noise through the speakers ‘normal’ with Naim amplifiers?
Hiss from the speakers definitely
Buzz/hum - maybe check your cabling
(as a test power down the Rossini and see if it goes away)