Aleph 30 ground loop

I have an Aleph 30 that has a ground loop coming from the right channel interconnect. If I bump the cable it starts buzzing, twisting the connector at the amp or wiggling the cable can make it go away. What should I be checking to eliminate it?

Source is TT, into Pioneer SX1500TD as preamp, aleph 30, epi 100 speakers.
 
The barrel of an RCA jack can become shorted to the chassis if the little plastic gaskets used to isolate that barrel from the hole are flipped around or swapped, or if there's a metal burr, or if the barrel has shifted in a big hole to the point of contact.
 
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