I have a problem with my S70 draining the battery overnight. Firstly I have bought a new battery so that's not the problem. When I switch on the ignition and wait before trying to start I hear a whining noise from under the hood up front on drivers side and when it stops there is a louder click. Not sure if this has anything to do with the problem as it would usually start first time and I would not be listening for any sounds.
Any ideas ?

 

The whining sounds like the vacuum pump (used to build brake boost on start up). Also, there's a guide on the 850 board on how to check for battery drain - you'll need a VOM that can measure current, then start pulling fuses to see if you can ID a circuit. Quite often it turns out to be a bulb in the glove box or a vanity light or power antenna that's not shutting off with the key or it could be relay etc. You should be able to find a Youtube vid or two as well.

 

Thanks mt6127 will have a look