Helping my child sleep

Hi everyone, I was hoping someone might have some helpful advice for me!

My daughter is 7 and on the mild end of the spectrum, but one issue she does have is that she cant sleep in a completely silent room, she seems to need some kind of 'hum' in the background - the sort of thing that would drive me mad while I was trying to sleep! She currently has a fish tank with a bubble pump running in her room and that has been working great, but this needs to be replaced and I dont really want more fish! Does anyone know if you can get 'fake' fish tanks or anything similar!

In the summer, a fan running in her room also works, but this leads to a bigger problem when it gets colder and the noise disappears.

I have seen the sensory fish tubes, but I dont know if they make any noise plus they are so expensive and I cant afford one.

Thank you in advance :)