Chirp type noise on hook up

Before I try reading the many manuals I wonder if anybody could point me in the direction of a chirping type noise I here periodically in my Corinium Duo, can't say when I noticed it as I have been busy on other things recently.

The vehicle is parked up outside my house connected to the mains via a hook up lead 24/7, the fridge/freezer says its on auto via the hook up and is cold so the 240V is functioning.

However the chirping noise is still present, when we went away in it a couple of months ago and on hook up there was no chirping.

I suspect that there's no link between being on mains, and the chirping. The most common chirping is, of course, an indicator of low voltage in a replaceable battery - e.g. CO2 alarm or smoke alarm. It's possible that on a 2021 van there are other items similarly powered.

We get one Beep from the microwave when we connect to mains; it's useful to hear it from outside the van, as confirmation of successful connection. But that's not. recurring chirp.

Cymro

Hi, 
Had similar noise intermittent from the co alarm above rear door on my 2 year old Fairford , took sometime to workout where it was coming from, the alarm had a non replaceable battery, couldn’t switch it off, didn’t have the little bent pin, made a bent two legged pin to shut it up, contacted alarm company who replaced by return of post because the battery should last I think 6 years. If you saved the little pin for shutting up just insert it and contact I think it was Angel.
John Dean