Computers on my network are clean for viruses and malware but still opening these files on the network is relatively slow.
What is confusing is that computers not accessing a network share are working just fine.
That's hard to say without knowing the full infrastructure.
What OS are the server & clients running? What protocol are the clients using to access the share? Details about the server storage e.g. RAID Level, internal or external, connector (USB, FC, iSCSI).
You have already ruled out the clients, that is a good start. Is it a purely Excel or Office related issue or is it general with files residing on the network share? Test some other files like PDFs, images if they are effected.
Another good start is analyzing bandwidth and throughput between client(s) and server using iperf. This will tell you if it is a network infrastructure issue
It is also a good idea to test the storage throughput directly on the server.
For Linux you can do this in the terminal using hdparm
"hdparm -tT /dev/sda" (replace /dev/sda with the appropriate storage device of course)
On Windows you could use HD Tune or ATTO Disk Benchmark (registration required, but tool is free)
I this should help you narrow down where the slow-downs happen.
OP should probably also check the server and network load. This can be done using Performance Monitor on the server by looking at CPU, disk, and network counters on Windows.
It would also be good to know if this is an intermittent issue (server/network load issues), if it affects only a few files (failing disk issues?), and exactly what is meant by "relatively slow."
A computer that is running Windows 7 or Windows Server 2008 R2 takes four minutes to open a Microsoft Office 2003 document from a network share
"0x000000D5" Stop error when you run an application or transfer some data from a shared DVD disc on a server in Windows 7 or Windows Server 2008 R2
1) disable SMB for Windows Vista, Windows 7
sc.exe config lanmanworkstation depend= bowser/mrxsmb10/nsi
sc.exe config mrxsmb20 start= disabled
2) disable SMB server
Registry entry: SMB2
REG_DWORD: 0 = Disabled