I would just unplug it. Bettas are labyrinth fish and do not require dissolved oxygen as other non anataboids do. They are able to breath air through the surface of the water, they can attain a small amount of oxygen from the water. But it's completely unneeded
I put that non skid shelf liner under the whisper 3i pumps. Make sure that the hose isn't touching anything too and the pump is pretty quiet.
Unplug it if the noise still drives you crazy for the night then plug it back in when you wake up. If you are doing regular maintenance on your tank having the filter unplugged for a few hours won't make a big difference.
What I don't know for sure is how long your beneficial bacteria have in still water before they die off. Maybe someone can help with that? (I don't know how long you sleep.)
I think I have this shelf-liner stuff lying around the house.. I'll dig it out right now and try it...
I sleep for 6-8 hours but the problem is that I can't unplug the stupid thing because the plug point is on the back of my dresser... i checked the hose and it's just the pump that is vibrating.. I'll let you guys know how the shelf-liner idea works...
I think your best bet is to just unplug and remove the filter. It sounds like it is giving you too much trouble. The main purpose of a filter in a small tank is to provide a place for the beneficial bacteria (what makes up a cycle) to grow. If you just do two water changes weekly it will eliminate the need for a cycle and therefor a filter in your tank. Filters really aren't needed in small tanks and mostly just blow the long fins of a betta around. The only way to keep your water clean is with water changes. Sadly, most people at pet stores don't know what they are talking about.