Have I forgotten what music sounds like?

Help, symphony experts. I have gradually been upgrading my system – new ARC LS-25 Mk II preamp, new Denon DVD-3910 – and I have noticed something interesting or maybe broken. I am not sure which.

I listen almost exclusively to classical music. With large-scale music, symphonic or choral I hear what can only be described as a “thrumming” sound from low frequency tones, mostly from brass instruments and the occasional pipe organ. Sometimes I think it is coming also from the double basses, but I’m but sure about that. It always occurs with sustained notes; that is, holding down a key on an organ or holding a note on a brass instrument.

When I first noticed it about ten days ago after adding the LS-25, I though for certain that there was something wrong with my system. So I did the engineering test thing, replaced every item one at a time to attempt to isolate the problem to a particular component, and always using the same couple of pieces of music. In every case that characteristic I’ve described remained present. I also attempted to identify any ground loop issues, and found none; it’s not really a 60 Hz hum in any event. I should say also that I never hear this with high frequency or fast transient sounds – violin or tympani.
I have pretty much convinced myself that this is really in the music. It’s been more than ten years since I’ve heard any live orchestral music – my bad – and it appears I have forgotten what the real thing sounds like!

I’d like to hear from any regular symphony goers out there, is it the music? I know it’s a kind of dumb question, so I promise as penance for asking it I’ll go to a concert. And yes, I know, this is audiophilia run amok – obsession with the sound of the system rather than focusing on the sound of the music.

Rest of the system; ML Aeon i speakers, Krell Showcase Amp, Meridian 568.2, and Audioquest cables throughout.

Bob R.