Welcome to your first post..
There are a lot of knowledgeable people here, but in order to answer your question, you need to provide a little info to start with. It would be like me asking you "why is my hand blue?". Can you answer my question without any additional info?
To start with. You should provide details about the hardware your host is running (memory, processor, hard drive size/speed/type, OS). Second, the same for how your VM is configured. It never hurts to post the *.vmx file and the log file along with your question. Search this forum there are plenty of examples of this information.
Is your hard drive "always busy" without the vm running?
What's the CPU utilization in task manager while this is happening?
Which process has the highest utilization at that time?
Do you have antivirus software running on the host?