What could cause axle to vibrate violently when taking off fast

What is your question?

I have a 2005 BMW 545i that has been sitting in storage for two years. It has been fine the last 3 months I've had it out but just started to do this. When taking off fast it feels and sounds like the axle is about to bust apart. It shakes violently until I take my foot off the gas. It only does it sometimes as of now but would like to find out what's wrong before it becomes major. Could it be low on fluid in the pumpkin? It's err wheel drive. Thank you

What makes this problem better or worse?

Taking off fast

How long has your 2005 BMW 545i had this problem?

Today