Hi Andy and welcome to the forum!
Looks like a possible infection to me.
For starters, download, install, update and run Malwarebytes Antimalware
Do the complete scan. It could take quite some time so go kill some time while the scan is running.
If Malwarebytes finds anything let it remove it and reboot if prompted to do so
I am not a malware specialist so if this does not resolve your problem pls post back and we will get you moved to the correct forum.