Is ground noise really normal? If so, why?

Alas, my tone arm is not balanced as I didn’t know it was an option. So while the P5XE feeds the rest of my stack in balanced mode, the tonearm wiring is good old hummy. I’ve to a spool of low voltage wire on the way (remember how great it was to have old radio shack around for that sort of thing?), maybe I can get rid of the noise by grounding the chassis in a few more spots,

Intermediatic, Tonearms (and the vast majority of cartridges) are indiscriminate.  You will have four wires from the headshell plug going either to a DIN plug out or some similar output plug.  If there is a DIN plug or some other similar type of termination at the back of the tonearm, all you need is a true balanced phono cable complete with XLR connectors, and you can then plug that into your Ayre.  There should be a DIN connector (or similar, but typically a DIN) at the tonearm end of the balanced cable.  The maker of the cable will have wired up that DIN plug to carry the signal in balanced mode to the XLRs.  Everything else is the same, NO re-wiring of your tonearm is needed. Get an inexpensive Audioquest or Anti-cable balanced phono cable (specify "balanced") with XLRs at one end and a female DIN plug at the other, and Bob's your uncle. (I specify those two companies only because they give good bang for buck and they can be relied upon not to sell you a single-ended cable that merely has XLR terminations.)

Ground noise is absolutely NOT normal.  I have many receivers and preamps and none of them exhibits ground noise.

Your phono section should be silent between tracks.  With no record playing and your gain turned up it should again be silent.  It’s like that on my Sansui 9090db, marantz 24, 1030 and 7, and completely black on my Phase Linear 4000 series one preamp.

Check your cartridge wiring (some tone arms differ in wiring configuration i.e. SME vs Grace).  Make sure the arm is properly grounded as should be the motor unit of the turntable itself..

Ground noise or hum would drive me nuts.  You may even have a bad cartridge lead.  

N.

Well, it took a while (and longer for me to respond), but I figured out that it was my Ayre phono preamp. They repaired it and now it's 100%. And paired with a Viella V12!