Disks on Michell Hydro Ref seem magnitized

I'm using a Grado cart. with J.A. Mitchell Hydro Transcriptor and am picking up noise as the gold "pucks" pass the cart. What can I do?
I think the "gold pucks" may be plated brass, which is non-magnetic so if that's true it would be very unlikely that they would induce hum/noise. On the other hand, many Grado cartridges are known to be susceptible to picking up noise.

There are many sources of noise such as motor interference, radio (RFI) interference, problems with the phono stage, etc.

But if you write to Michell I think they will confirm that those discs are non-magnetic and not the problem.