[X4U] Hard drive space

[Robert]

Over the past couple of weeks I have been running out of hard drive  
space. If I restart I have 39 gb. With out running any apps My hard  
drive space starts to go down. I can hear the hard drive running. In  
the time to write this email its now down to 37.32 gb. In roughly an  
hour I or 2 will be down to mb. Then I get the message that I'm out of  
space. So much that mail quits as it can't save anything. If I restart  
I get 39 gb of space back.  Mac pro running 10.5.1 with 5 gb ram. If I  
run Activity monitor ->Disk activity Data read and data written the  
graph looks like the alps. Nothing looks out of place under process  
name. At this moment I'm down to 35.46 gb and dropping. Any ideas.  
Thanks in advance. Bob