I recently had a DiMarzio D-activator Bridge humbucker installed in my RG. There was already a PAF Pro neck humbucker in the neck position. When I went to pick up the guitar after the installation, it hummed like an angry wasp. The bridge pickup made no noise whatsoever, but the neck pickup and coil tap positions were just plain bad. The guitar tech at the shop claimed it hummed because the PAf Pro uses alnico 5 magnets and the D-activator uses ceramic magnets. A friend of mine said the hum is most likely caused by improper grounding.

So my question is, do alnico 5 magnets hum severely when they are in a guitar with ceramic magnets?
I don't think so.... Grounding seems more likely to me
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sounds like a case of him not admitting that he cannot change pickups and just wanted your money so he makes up some bullshit so you dont demand a refund...
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Bad grounding. Go get your money back and either ask for help here to fix it yourself or have your friend do it since he seems to know what he's talking about.
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ok. Thanks for the advice everyone. I emailed DiMarzio about it and they said ceramic pups make less noise than alnico pickups, but I know a ton of people who have the same magnet combo in their guitars and they don't have this issue.
Ok I think I can find a better tech. But getting the instrument back without the idiot tech demanding payment for the job is going to be difficult. Anyway, thanks everyone for the advice!