fuel relay on way out?

[Cymru1]

Strange one.

All fine now but the other day i switched off and walked away, when i heard a "hiss" (similar to a boiling rad).
Opened the bonnet and the "hiss" was coming from the return pipe on the fuel rail.
Checked the boot and sure enough there was a constant "hum" (pump?) which could only be stopped by disconnecting the battery. ?
Any thoughts? Relay?

Never happened before and all fine since.

[terrybullwon]

Sticky relay could we be it!, pull the top off and take a gander, I have a new one here if you need it