I have had one of these, bought 2nd hand off ebay, for ages.

Used for vocals, of course.

Never had a moment's trouble with it.

Don't understand the "Guitar Center" unless of recent units are of junk quality. Mine is a metal box, built like a tank. I had open it and change a jumper to use 220v power (not a credit to ART, a standard screwdriver slot switch would have been a better idea, and, as usual, "no user servicable parts inside. After almost destroy the unit with my grubby hands, still works, no noise).

12AX7 tubes are around, in demand and special quality tubes are available to get that special compression, but the hum is from elsewhere.

Check for ground loops in your setup.

The ART uses full sized connectors, the computer interfaces use minis which usually introduce noise.

Anyway, the album I did used an old Midiman2044 PCI interface with its chunky, fullsized connector breakout box. No noise. Still hoping someone will get this baby working on Linux.