This comes from BWV 847 (the C minor fugue from the Well Tempered Clavier).
Look at the third beat from measure 28.
I can't help but hear an A flat minor chord here, that is Eb, Cb, Ab. Especially when playing with an "organ" sound on a synthesizer or something rich (because of the harmonics of the Eb at the bass, I suppose). Try to add the Eb above middle C to the chord to see what I mean.
I know that the harmony is supposed to be a G dominant over the Eb (that is a vanilla V/I movement over the Eb), and you can suppress any tentative to think otherwise by adding the D to the chord (I even have an edition at home which suggest that there is at least one manuscript where the copier added this D).
Am I the only one to hear this "C flat" ? Is there any actual example of chromatic mediant movement in Bach by the way ? Would you add the D to the chord ?
EDIT: here I can hear it a lot :(at 3:28)