Lyra Lydian Beta, Rega hum?

Still think it's the cartridge, but one other possibility has occured to me. Is the cable from the phono stage to your line stage shielded? If not, this can be a considerable source of hum. Let us know how this turns out.

Can't help wondering if the hum is due to an open coil in the cartridge. Is the hum so loud that you can't listen to music and does it begin the second you engage the phono circuit? If so, it may be an open coil problem. This happens from time to time with less expensive cartridges as quality control is usually less then with the ultra expensive cartridges. I had this problem with a blue point special and grounded everything in sight(boy, the dog sure hated that wire around his neck) until I gave up and had the cartridge tested, found defective and replaced with end of problem. Sounds like it's time to take the cartrige back to the dealer or if no dealer, Immedia and let them check it out.