Could not connect to localhost:9000

I am running Ubuntu 18.04 in Windows Subsystem for Linux. When I try to "sudo apt-get update" , I have the following error:

myuser@GA014291L:/mnt/c/Users/myuser$ sudo apt-get update
Err:1 bionic InRelease Could not connect to localhost:9000 (127.0.0.1). - connect (111: Connection refused)
Err:2 bionic-security InRelease Could not connect to localhost:9000 (127.0.0.1). - connect (111: Connection refused)
Err:3 bionic-updates InRelease Unable to connect to localhost:9000:
Err:4 bionic-backports InRelease Unable to connect to localhost:9000:
Reading package lists... Done
W: Failed to fetch Could not connect to localhost:9000 (127.0.0.1). - connect (111: Connection refused)

I can ping my local Windows OS, as well as google.com with success.

Any idea, how to resolve this?

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