As these appear to be songs you have sourced from Records (Vinyl), I would suggest cleaning them up one by one rather than run an automated process over the lot, as some songs will have a lot more hiss and crackling than others depending on the quality of the record and how scratched, dusty and worn it is.
Audacity is one of my preferred for its range of features and is also freeware, which can be downloaded here. I would also recommend getting its LADSPA plugins from the download page.
Before working on your recordings, I would strongly recommend making a backup copy of them, in case you need to redo an operation later on.
The following is just a very quick guide if you haven't used it before:
- You will find the click and noise removal tools in the Effect menu -> Utility -> Noise Removal.
- For the Click removal, try the default values first, click 'Preview' and then try adjusting the individual values up & down to see what affect it has on the music and clicks. Be careful not to harm wanted audio, e.g. percussion instruments.
- Before you use the noise removal, select a few seconds of silence (e.g. just before the song starts), then go into the tool and click "Get Noise Profile". Finally, select the entire track, go back into the tool and try the default values and preview the effect. Depending on the noise and music, it may be worth tweaking the values to see which works better/worse for the current song.
- To delete unwanted audio at the start & finish, select the silent part at the start, press "Delete" on the keyboard and repeat for the silent part at the end.
- Finally, to normalise the track such that each track you work on ends up with roughly the same sound level, select the entire track, go into the Effect menu -> Amplifier -> Normalize, leave the options as they are and click 'OK'.
- To save the track as MP3 (requires Lame MP3 encoder) or WAV, go into File and select "Export...".
Another utility I've used in the past for repairing recordings from records is Goldwave, which can be downloaded here. I find it more user friendly and also very good at cleaning noise, crackling and pops from records, but the software is not freeware. From what I recall, the trial version is limited to 150 commands per session and 4,000 commands before it expires, so it's worth a try.