My turntable hums as soon as I lower the tonearm

[Balle Clorin]

Had the same issue, but then the ground wire was not attached as I thought..

 

[Palmer]

Odd. Almost like you had a contact that was not, erm, making contact, and now it is... Hope it stays problem free

 

[rdenney]

Late hit, but for posterity:

Air handling motor on your air-conditioning system. It will vibrate the whole house at a very low level.

Rick “I could show you pictures from my REW graphs” Denney