Could you let me know what model iPhone you are using?
And try this!
Record a video and see if the sound is funny.
If it is then you know that there is something wrong with the top microphone.
Next open up voice memo and record something.
If it sounds funny then there is something wrong with the bottom microphone.
If both of them sound funny it could be something with the software on the phone.
If both of them sound like that I would suggest a software restore!