Eng relay buzzing on 94 V6

[Chucky]

Guys,
Helping a mate on his 94 V6 Paj and when teh key in the off position the eng relay (Located behind the dash speaker on teh passenger side) Buzzes. The buzz is like a relay chatter and if let alone it will enventually flatten the car battery. When the key is in the acc postion of in the ignition postion it the buzzing stops and the car works (starts and drives as normal). When the key is switched off the buzzing will start about 5 secs after the key is turned off.
I have gone over the car looking for loose plugs and any obvious shorts and can't find anything.
I also know 100% that the eng relay is the cause as when you unplug it the noise stops and when you are holding it while plugged in you can feel the contacts chattering. This also happens with a brand new relay as well as the old one so I know the relay isn't the issue.

Checking the plug, I have identifed the terminal that earths out when the switch is turned off, 12v power is constant to the relay and seems to be negitively switched.

Any help or a heads up on what to look for would be a great help as I know nothing about these cars.


Thanks in advance.

Dan