The clicking sound coming from the iPod usually means its hard drive is faulty. You can try putting it in Disk Mode
Putting iPod into Disk Mode - Apple Support
Then run iTunes and connect iPod. If iTunes picks it up, it may prompt you to do a Restore. The Restore erases the iPod, reinstalls its software, and sets it to default settings. If the iPod does not go into Disk Mode, or the Restore fails, the iPod probably has a faulty hard drive.
If your iPod is in otherwise good shape, you can consider replacing its bad hard drive with commonly available (and affordable) flash-based storage in the form of Compact Flash card or SD card, on an adapter. This web site has relevant information, if your iPod classic is 5th gen or later.
https://www.iflash.xyz/
I have not used these particular adapters (because my "classic" iPods are older than 5th gen), but I have done the equivalent mod on my older 3rd gen iPod, 4th gen iPod, and iPod mini (using different adapters). They are working better now than when they were new, with much higher storage capacity.