Veritas backup too slow

Hello, we are puzzled by the slow job rate of our large backup. We are running Veritas Backup Exec 9.1 (Rev. 4691)on a Windows 2000 Terminal Server platform.
With 4 gb of memory and 20 gb of disk space.
We are backing up (7) servers (database, file, exchange servers)to tape.
Our last normal job rate was successful at a total of 173 mb/min.
Currently, the job rate is at 130. Please help us regarding this problem. Thanks!
P.S. We are also using our Exchange Server to link to one mass storage device that maintains (5)volumes.