There comes a time when most every video producer has the need for one or more sound effects to finish out their latest production. Hal Robertson with Videomaker has a valuable post on this topic in the Videomaker magazine on-line, here's a snippet:
Many many people are looking for sound effects for free and if you just Google "free sound effects", that would bring up tens of millions of hits.
However, you'd have no idea which were useful, let alone legal. The pirate sites are off limits so you need a way to sift through all the free sound effects downloads to find those that fit your budget and criteria. Free sound effects are out there, but it's important to find the ones that are truly free, of good quality and meet the needs of your project, all at the same time
You can read the entire article in this Videomaker on-line article: Free Sound Effects.