[AverageNiceGuy]

This is YouTube link to a 20-20kz changing test tone.
It is helping me to find things in the room that rattle.

It also helped me to notice a 250hz rattle in one of my woofers. The woofer edge was a little loose, and was rattling against the speaker box.

https://www.youtube.com/watch?v=URrEtyFSENc

The second link is for a constant 250hz tone that helped me as I poked around to find the source.
https://www.youtube.com/watch?v=WLTo9ePFMo4

[Hobbsmeerkat]

I like using this tone generator, since it also allows you to use different types of tones including square & sawtooth waves, and you don't have to worry about YouTube's compression algorithm, esp at higher frequencies.

https://www.szynalski.com/tone-generator/

[WGH]

Audiocheck.net has test tones both online and for $5 you can download the uncompressed .wav files for every test with increased durations and sample rates up to 192 kHz in the Tone Gen section.
https://www.audiocheck.net/audiotests_index.php

[AverageNiceGuy]

Those are cool. Thanks