Incompetech Royalty Free Music http://incompetech.com/music
Find Sounds http://www.findsounds.com
Partners in Rhyme https://www.partnersinrhyme.com
Free Sound Effects http://www.pacdv.com/sounds/index.html
Free Music Archive http://freemusicarchive.org
Creative Commons https://search.creativecommons.org
BBC Sound Effects https://sound-effects.bbcrewind.co.uk/
All sites require correct citation.