Back in the 60s, when XLR jacks where still called Cannon jacks, the standard was pin 3 hot (not 2) pin 1 ground (just like now) and pin 3 cold. Since the XLR jack is wired for unbalanced use, what Grog describes is is correct for the time.
Normally vintage wired XLRs can be used as is with modern gear as long as you are not concernned with it causing a 180 degree phase shift (or if a devise in the signal chain has a polarity reverse switch). Otherwise, or in such an unbalanced case as this, it would be best to reverse the wiring so that pin 2 is hot and pins 1, 3 and chassis ground tied together.... or as Grog did, reverse wire a cable so that the input device (amp or PA mixer) is not seeing pin 2 (tip on the 1/4" jack), tied to ground at the guitar, which would totally explain the noise.