Whistling noise after cleaning galvo mirrors

I cleaned my form 1+ galvo and small mirrors today, after that the printer starting humming with a high pitch whistle that wasn’t there before. The print seems to be going normal but it’s just that annoying whistle, did anyone have this problem before ?

https://youtu.be/ieHY63DScJM

I took off the back cover and put it back again, the whistle is now gone

The little guy must have jumped out.