RedGIFs began as a home for GIF-style loops, and a big share of clips are still uploaded with no audio track at all. So "no sound" usually isn't a download problem — the clip never had any. Here's how to tell the difference.
Paste the link into RedGIFs Downloader. Next to the length and resolution, the card says with sound or no sound. That comes straight from RedGIFs' data for the clip, so it's the same answer you'd get on RedGIFs.
Open the file in VLC → Tools → Codec Information. A clip with sound lists two streams: video (H.264) and audio (AAC). One stream means the file has no audio.
Open RedGIFs Downloader →No. RedGIFs started as a GIF host and many clips are uploaded without an audio track. Clips that have audio keep it when you download the MP4.
RedGIFs Downloader shows 'with sound' or 'no sound' on the result card, read from RedGIFs' own data for that clip.
Check the player isn't muted (RedGIFs and many players start muted), and make sure you saved the HD or SD MP4 and not a GIF conversion, which never has sound.