Mystery Relay

Hi.  After a recent drive and setting up i have ad an annoying  noise from a relay that sounds just like the old flashing indicator units. Some thing is triggering the relay to switch on and off repeatedly. My van is a 2011 symbol. the relay is situated in the battery/water heater compartment beneath the bench seat. it is a 30 amp with wiring that bears no relation to diagram supplied by autosleeper. 
I disconnected most  habitation devices one by one to no avail. the switching did stop eventually but I don't think it was because of my actions. It has not returned (yet) but I would like to know what the function of the relay is for future reference. Can any one help?
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I'd probably start by taking the relay out and then seeing what stops working 

RogerThat wrote:I'd probably start by taking the relay out and then seeing what stops working 

I did that and could not link it to any of the normal habitation system

PLOUGHLIN wrote:Could be the relay for the Fresh water tank float arm?

Interesting idea.  The tank was near full but I had used some. Would a simple sensor need a relay?

PLOUGHLIN wrote:

mossystone wrote:

PLOUGHLIN wrote:Could be the relay for the Fresh water tank float arm?

Interesting idea.  The tank was near full but I had used some. Would a simple sensor need a relay?

Not the sensor, but the loat arm which cuts supply to the inlet socket when full (whale and Truma water fill systems).

Aha     I could test that by listening while filling the tank.  Thanks.  Will follow that up.

The float switch that operates the solenoid valve on the water inlet cannot carry the current needed so the relay is added to the circuit. When the tank is nearly full and you walk around the van the float moves up and down and the relay chatters in sympathy. If that annoys you, drain some water.

That's brilliant.  It explains why it stopped.   Thank you for all your responses. I can stop worrying now.