My land rover discover 2000 has some issue:-

1. SLS warning lamp is On.
2. Underneath it has box which makes like something On/Off sound 24 hrs but you can't sleep at night hour because the sound is clear something hammering metal (it works like change over for the electricity when contacting phase to onther phase).

 

Welcome to the forum, moved this to the right place so you might get help

 

What fault codes are you getting for the SLS light to illuminate?
24 hour hammering noise??? With the ignition key turned off? Open your hood/bonnet and check the IAC valve on the top back part of the engine. Feel it to see if that is the culprit to the hammering/buzzing noise. It's supposed to make a buzzing noise when the ignition key is turned on.

 

 

To check if it is the compressor for the rear air suspension, try pulling relay #5 from the fuse box under the hood. I believe that fuse #9 is also part of the same system. If the noise stops when you remove either of those parts, there is a fault with your air suspension system.

 

X1 ........... agreed. Plenty on Ebay and cheap. Don't forget to clean or replace the air intake filter behind the drivers side rear light it's the most overlooked air filter.

Are your SLS air suspension bags leaking air? It is often the case when the rear suspension 'drops down' overnight.