Others have brought up good troubleshooting tips so far, like disabling your voice chat key binding or double-checking that your controller isn't disconnecting and reconnecting mid-match. However, your game logs may also help us understand why these random stutters happen.
If you can, could you please DM me your game logs? You can find them in the directory:
C:\Users\%USERNAME%\Documents\My Games\Rocket League\TAGame\Logs