Hi, I use the YouTube Audio Library. Login to your YouTube account then click on your account icon at the top right. Select YouTube Studio. Then in the left hand pane scroll to the bottom and select Audio Library. There are tabs for Free Music and Sound Effects and one called Starred for you to store tracks that you like and 'star'. Download any tracks that you like but remember to look in the Licence column to see whether attribution is required or not. If Creative Commons attribution is required then copy the precise text and paste it into the description below your YouTube video. I personally always attribute the music artist because I think it is only good manners to acknowledge others' contributions.