Cartridge problem: Lick it. It works.
3DS problem: Get a new 3DS, because yours sounds pretty beat up.
This is poor advice as your saliva will corrode both the cartridge and the system's contacts.
Hmm... it could be a combination of the DS and cartridge.
Show us a photo? Most people on here know what a worn out cartridge looks like.
One thing you could try doing is putting a few layers of tape (just use trial-and-error - there are too many factors for me to give an accurate number) over the front of the cartridge, where the label has been pasted. This will make the cartridge press against your system's contacts harder which should prevent the issues you are having.
If the contacts on your cartridge are severely worn down then I've heard you can use a small amount of conductive ink to get them working again. I have no idea how safe or reliable this is though, and you should make sure to never have a connection going between any of the seventeen connectors.
- - - Post Merge - - -
I'm worried about one of my game carts myself because you can hear something rattle inside when you move it around and it makes me nervous. I hope something inside the cart didn't break, though the game still works. None of my other game carts for anything make a rattle sound so I'm freaking a bit.
Oh, that's fine. Around half of my DS games rattle with the most played one and one of the less played ones, Metroid Prime Pinball and Solitaire DS, being the worst. I've had
zero issues with them so you'll be just fine.
Disney Pixar Cars (DS - UK) - No rattle
More Brain Training from Dr Kawashima How Old is Your Brain? (DS - UK) - Rattles
Tetris Party Deluxe (DS - UK) - No rattle
Pok?mon White Version (DS - UK) - Rattles
Space Invaders Extreme (DS - UK) - Rattles only at specific angles
Metroid Prime Pinball (DS - UK) - Rattles
Mario Kart DS (DS - UK) - Rattles
Sonic Rush (DS - UK) - No rattle
Mario vs. Donkey Kong Mini-Land Mayhem! (DS - USA) - No rattle
Spectrobes (DS - USA) - No rattle
Countdown The Game (DS - UK) - No rattle
Solitaire DS (DS - Spain) - Rattles
Disney Club Penguin Elite Penguin Force (DS - UK) - Rattles
Super Street Fighter IV 3D Edition (3DS - UK) - No rattle
Mario Kart 7 (3DS - UK) - No rattle
Animal Crossing Wild World (DS - UK) - Rattles
Animal Crossing New Leaf (3DS - UK) - No rattle
I'm wanting rid of a lot of those games but it's too much work selling them, lol.