I have a lexmark x5320 after I receive a telephone call my printer hums until it power it off and back on, is there a filter of some type I should be using?

My random thoughts:

It could be that the incoming phone call simply "wakes up" your printer from the sleep mode. See if it goes back to sleep after 30 minutes or so.

If you have DSL for your internet, you would need a DSL filter, just like on your other phones.

Next time it happens, try unplugging just the phone line connection to the printer and see if that makes the hum go away.

Hope these help!
WallyH