Very quiet, actually.
If for any reason you are in London and are struggling with the virus, please be aware that buses may not be entered at the front (to protect the driver).
Use the middle door, let other passengers off first (at a sensible distance), there’s no need to swipe in and take your time as there’s no hurry.
Bus doors have big stickers on telling you what do to. And do spread out inside the bus.
Even better, stay home.