Well basically my friend (nirtoninjao_0) has her own server its not public yet so we've been building things on there. usually I go offline before her. When I went offline about 10 - 15 minuets later she was still building our 'prom' we had disco lights and a jukebox (nothing was in there) and nirt was using world edit to remove a sphere (that i randomly did :P ) then she heard footsteps around her then the song 'wait' started to play from inside the prom.
Nirt then she heard footsteps from underneath the disco lights a few seconds later she heard the redstone being smashed, they had...
So she typed "who's there?" after about 10 seconds the steps began again!! She typed "Hello?" there was no reply.
At this time nirt was extremely confused, So she started to record, a soon as she started to record EVERYTHING had stopped instantly! She thought it had stopped It had.
About 2 days later she went back to prom. everything was normal... Until she saw a massive 'n00b hole' but it had gone straight down to the void, and when you start off you're in survival so a player couldn't of done it either.
Using server things she look at cmd.exe and no one had logged in or logged out either.
Then on the 16/12/12 I was the only one one the server and I was working on the Zeppelin and random blocks were being remove then placed so I went back (quite far) and it was still happening so I typed "Hello?" it carried on then I typed "Anyone?" Then it stopped I was SO confused.

then on 23/12/12 nirt heard sheep, cows and chickens being killed and grass being removed. but this time I was on the server but I was AFK in the sky i was afk for about 2 hours ( i thought i had disconnected) so nirt thought it was me so she tped to me about 4 times and i didn't move obviously then nirt was really scared!!

If anyone knows what's happening PLEASE tell me or nirtoninjao_0 :)
!!