Strange noise from rear of car when engine off, but drawing power

[Z4chippyme]

Z4 E85 2007, 90k on the clock... I have a strange noise from rear of boot... sounds like the tyres are leaking initially but when you listen inside boot or near tyres it sounds like something electric or a fan blowing. The battery is being drained empty, but when I turn ignition on, the noise stops total silence. I've started taking the red lead off the battery, to stop it draining and kill whatever is still running. I just purchased a new battery thinking the battery was dead ... Any ideas what this could be? Do I need to reset the computer after the battery was replaced, is this something I can do with the Key fob ?? either way, the noise continues unless i kill the battery. If I leave it connected, eventually the alarm goes off, I guess telling me the battery is dying? Help?

[B21]

Z4 E85 2007, 90k on the clock... I have a strange noise from rear of boot... sounds like the tyres are leaking initially but when you listen inside boot or near tyres it sounds like something electric or a fan blowing. The battery is being drained empty, but when I turn ignition on, the noise stops total silence. I've started taking the red lead of the battery, having just purchased a new battery thinking it was the battery... Any ideas what this could be? Do I need to reset the computer after the battery was replaced, is this something I can do with the Key fob ?? either way, the noise continues unless i kill the battery. If I leave it connected, eventually the alarm goes off, I guess telling me the battery is dying? Help?

Best post this in the E85 section…not many G29 owners are going to be au fait with this issue,,