Hi Desbug_85_
Re: "Noises coming from my phone" "it occurred when I wasn’t even using it"
Wondering if there could be notifications set to appear on the Lock Screen.
Re: "I also heard a noise that sounded like someone was sipping out of a drink"
Was that the sound we hear when an e-mail is sent ... (sometimes there is a delay in an e-mail leaving a device, especially if it has a large attachment).
Re: "I’m wondering if somebody can see or be listening to me".
If you wish, you can:
Get help with security issues – Apple Support
or
Contact Apple for help with Apple ID account security – Apple Support
Apple also has a Personal Safety User Guide – Apple Support. online.
All the best :-)