Odd noise when charging battery

Hello all.
I have been charging my battery to keep it happy.
Using a CTEK smart charger and after connecting up i get a strange thumping noise from the rear air bag compressor under the passenger side. I am not sure why...any ideas please?
I checked the rear of the car and mid point on rear mudguard it measures 89cm from the ground with 256x65 x 16 inch tyres.Bags look inflated.It does not make this noise without the charger being on.

I have disconnected the earth lead to charge the battery in the interim.
thank you

Hi Westone, I've just bought one of these chargers too (MXS 5.0) but haven't connected it yet as I use the vehicle every other week . Will be interested to see the replies.
Griff

Will I changed it to my 25 year old Challenger model battery charger and the noise stopped.To be fair I used the CTEK on my old Disco and had no problem...its odd.
I wondered if being digital made a difference.
A very good write up on here about the SLS system I read.

When I disconnect my battery for a time then reconnect, i get this for a journey or 2. The compressor runs on after ignition is off and pulses 2 or 3 times. Then its fine again until battery comes off.
If i recall it was suggested its a SLABS gremlin. Not usual behaviour but it doesn’t really cause any issues.
It may be your charger is also causing the SLABS ecu to throw a wobbler. Ive no idea why though.

Thank you ronsealdeath...I am a bit concerned about my whole SLS system as read on the forum the air bags should be changed every 5 years and I do not know the age of mine, cannot find any leaks anywhere , but its next job to go over the whole system.Battery all charged now to 13.72 volts,I expect it will drop back a bit in the morning.I did wonder if the compressor was trying to break out!

When driving, do you find the car tries to level itself at junctions if at a camber? Or if parking in a hill? If so, you may have this SLABS gremlin, so to speak. When you are dealing with cars at this age, these things do happen. I dont find it any issue to be honest, but you are right that if your bags look old, then changing them is a good idea. Height sensors are also sensible to change. As always, use quality parts (conti bags etc).
Get a schrader valve emergency kit too, if you haven’t already. Peace of mind
https://www.ebay.co.uk/itm/272726607403

Thank you for that posting I will get a kit, did not know about these, it does seem to level it self on hills.The rear looks lower to me than the front, but it may be me,I keep measuring it with a tape.I have heard some scare stories about folk buying cheap bags and they then leak,I will get some good ones.I did have the amber warning light(with arrows up and down) come on one day when i had changed from high to low and then back in the gearbox,I am not sure if this was related.
I stopped the car switched off and upon re start it had gone off....not come back on. I have changed the sensors on my old TD5 once and I bought them from a LR dealer, very expensive but worked okay.I see them for sale on e bay ,but wonder if they would be any good.
Thanks again will update how i do

Can i ask please how you use the kit? probably being a bit thick.
thank you