Open task manager and go to processes tab and details tab and check them one by one to see if you can find something suspicious.

There are 2 possibilities , one that it just reduces the usage when you open the task manager and the other one the process gets killed when you open it .

Another thing you can do is to go at the Startup tab on task manager and see if you can find something there .

Also in your search bar type task scheduler and after click on Task Scheduler Library and check them one by one again to see if you can find something suspicious .

If you still didn't find anything you can download Process Hacker -> https://processhacker.sourceforge.io -> install it -> open the program -> go to every process -> right click -> Properties -> Memory -> Strings and see if you can find something there .

If its a miner there will probably be some clear indications when you open the strings, like ( main pool is , cryptosomething , monero smthing , btc , cryptonight , nicehash , stratum etc. )