Internet speed dropping after connecting ethernet cable

[MRin]

Hello, i got this problem:

Im having a 4 down & 0.5 upload connection, which is more then enough if it's stable.
Yet, I've realised that right after im plugging my ethernet cable to the PC, the speed drops a lot, mostly download. It goes from 4.1 / 0.5 to 0.1 / 0.3.
Im using win10 & checked on the resource monitor what is taking up my network speed on the PC. Yet, there are just the usual programs showing up which im using since years & they didn't had any update recently (online game & ts3). Even right after just starting my PC, not running any program, i can see the download speed graph dropping hard. Im making a speedtest at the same time on my smartphone via the speedtest app. Once i unplug it, the speed goes back to 4.1 /0.5.
I've aswell checked my PC on malware and found nothing (Using Avira). Was thinking that i may have a virus or smth which tries to connect or whatever.
My technical provider changed all the connections and ports already & can't find any mistake.

It's really strange, since sometimes the speed, even while connected to the PC is normal and out of nothing it drops like explained.

Thanks in forward for any helpfull answers & tips

[Geek-9pm]

Your tests show that a background program is using the Internet.

[askingforhelp]

Hi,

I am not an expert, but are you using Windows 10? My computer downloaded a large update recently for Windows 10. That might explain your issue

[MRin]

Well, i looked up what's taking up my internet connection with the help od Reaource Monitor & there was nothing. Do you think it could be a virus?

About the win10 update, it's strange since it happens sometimes after starting the PC & sometimes while using it for some hours.

[Rustys]

How may devices are connected to the network?

[MRin]

How may devices are connected to the network?

Usually just one, when i realise that im lagging i make the speedtest via my phone.

On the resource monitor though, i've realised that svchost.exe (some automatic windows background updates) use to take up some resources.

[Rustys]

Are you running WiFi or direct cable connect?

Are you running directly off the modem or is there a router?

Have you tried rebooting the Modem, router (if there is one) to see if that refreshes the network?

[Lorraine walsh]

My probable guess would be if f you have an old NIC card around I would try it, to see how it goes and if the issue still on .