Long story short, nope, it seems to be a mix of sounds and audio and montage... Some people freaked out on Reddit as well, and a user who supposedly knows their way around sound mixing says there's a mixture of sounds giving that effect, but it's not an actual spoken line.
I've worked a bit in sound engineering (unprofessionally) and decided to do a bit of work on this "voice". I listened through this section probably about 100 times while EQing and adjusting the play speed and have concluded that the initial sound (the one that makes up the "I" sound people are hearing) is the beginning of a breath/sigh from Thor. Its frequencies match very closely to the sigh we hear later in the clip after he sets down Stormbreaker. [...]
TL;DR: Through some sound manipulation, it's likely we're hearing a set of noises that make up this "whisper". Another Yani/Laurel situation. [...] I'll have to experiment further, but this is DEFINITELY human pattern recognition.
Add to that that telepathy isn't in Captain Marvel's skillset (not her MCU version at least) and it didn't make it to the movie (it's a trailer montage thing). Sure, trailers have been shown to deliberately mess with viewers at times, but here... It would make zero sense. Stuff happens, and we hear a lot of things when we're hyped.