Noisey Relay In The Passenger Footwell

[sjray]

On my P reg UK Previa, there is a cluster of relays on the passenger side under the footwell. There are two metal relays and one of them (the top one) has started clicking randomly while driving. I've taken both out and reseated them but the top one is getting very warm.

Does any one know what these relays do and should it be noticeable when they click in?

Also, should I just replace the noisey one or is this an indication of another problem?

Thanks,

Steve