Depending on what you want sounds for:

1. If you just want Sound FX to use in your own personal projects, (Not for sale or resell), most sites let you use them for that.

2. Commercial Use, (For sale or resell), of Sound FX, usually requires the purchase of a license, whether it be one time, unlimited use, etc. If you just need a few FX, they are relatively inexpensive. Some from .50 on up to 3-4 bucks or more, each.

3. Google is a terrifc tool for researching Sound FX. Like I said before, several years ago, there was a lot of free stuff, but once everyone found out they could make a buck or two, most started to charge.

4. Public Domain....Most stuff, images, sounds, voices over 75 years old have copyrights which have expired or no copyrights at all...Again, depends on want you want. You can do a search for Sounds, Sound Files, Voice Recordings, Old time Radio, etc. Make sure you use something like Sound Files, Free or Sound Files, Public Domain.

5. For military sounds I search for specific sound files. Sounds, jet aircraft; sounds, military; sounds, f-100; etc.

6. Train webistes are usally good for locating trolley or train whistles and the like. Most historic train or trolley sites, have at least a few sound files. (You only need to check the terms of use).

7. Animals, etc: sounds, eagles; sounds, whales, etc. Most government agency sound files, images are in the public domain, but some also carry copyrighted images or sounds from professional photographers, etc.

8. US Fish and Wildlife for animal sounds is excellent.

9. Could also search BLM, Forest Service or State Agencies.

10. Do a little bit of research and you will be surprised what you can find. Just be awre of copyright infirngement and check out terms of use. Most gov. stuff either requires a notice of use such as Photograh by Sgt. Mac, or please credit US Fish and Wildlife Service...(Oh..and I have gotten good results through zoo's for animal sounds... Good luck!