Before you give up hope - try a few different carts - if you can. If they all hum about the same then you've a problem with the p25/600.
I personally couldn't tolerate the P25/600 with its earthing/motor shielding quirks and changed to another brand of t't; and haven't been happier.
I personally couldn't tolerate the P25/600 with its earthing/motor shielding quirks and changed to another brand of t't; and haven't been happier.