Noiseless aircraft

Hi everyone!
I have a question,
I have an ads-b site from 2 week, every days at 9:30-10 pm 2/3 aircraft pass above my house (center Italy) or very higher and very fast or very near and slow tbut: have only one white fix light and NO NOISE.
No tracking details from my site or other services… I can’t understand wath it is…
Someone can explain?
Thank you guys.

Could it be a glider perhaps?