Find the cause and repair the problem. You may also have to replace the foam rubber matting since it would be prone to mold if it has been wet and not completely dried out.
Try and get something to keep under the door and it should stop.
A leak. It could be a plumbing leak; are there any bathrooms or other plumbing nearby? It could also be a roof leak; don't rule that out! Another possibility is a leak from high ground water or foundation leak. Check everything you can think of.
To effectively stop squeaky floors under carpet, you can try using screws to secure the subfloor to the floor joists, or use specialized squeak-reducing products like shims or adhesive strips.
A leak (window / ac / floorboard etc.) may be allowing water in. Check the carpet's under the floor mat's for dampness. Finding the leak is another problem!
Repair the pipe of fixture to stop your leak.
It is best to use a thin, firm pad under the carpet to help stop ruts from forming. A low pile, dense carpet will also be more resistant to ruts as well. = =
To fix squeaky floors under carpet, you can try using screws to secure the subfloor to the floor joists. This can help eliminate the movement causing the squeaks. You can also use specialized squeak elimination kits that are designed to stop the noise without damaging the carpet.
Replace the line that is leaking, and do not try any stop leak.
A carpet pad goes under a carpet to provide cushioning and insulation.
An angle stop under the sink is used to control the flow of water to the faucet, allowing you to shut off the water supply in case of a leak or when performing maintenance or repairs.
A raw egg in to the tank.
A good stop leak product for a radiator is the Bar's line of stop leak. It comes in an easy to pour bottle which seeks out leaks and seals them in minutes.