My dryer shakes and rattles really bad! Never used to do this, now its so bad it shakes the house. Please help

Do not run the dryer until it's fixed; you lost the felt pad around drum I would guess. Since the pad came off, most likely it's dirty and lint deposits have built up, as it always does, in all the air ducts which can cause overheating, which causes the glue to melt on felt pad which comes off. It should have been cleaned yearly. A little vacuuming out does nothing. You will have to take it apart and clean it out thoroughly or it is all for nothing. Every air duct will have to be removed and scraped and washed out to remove baked on lint deposits which is like a concrete lining. This will burn so the manufacturer has installed the safeties to keep from having a house fire. Look at: http://www.youtube.com/watch?v=MMP7BW1lLs4 to see how. Also: http://www.youtube.com/watch?v=iBiRw-KElC4 ; http://www.youtube.com/watch?v=yFTZGgVisCI
http://www.electrical-forensics.com/Dryer/ElectricClothesDryers.html

When you finish cleaning the drier and install a new felt pad it is best to also replace the belt, too, because you do not want to have to disassemble it all over again and if the belt is over two years old you should replace it.

Note that on most of the videos it does not show them washing out the parts, but this is important because it's the only way to really get the parts clean, just don't get motor wet or the capacitor if it has one. Vacuum out the motor to remove all dust and clean blower wheel, too. I would move the drier out to your garage to have plenty of space to work. You also want to check your vent and clean it, also. The vent should have a short run and be straight as possible. The job is really easier than it sounds. There is no shortcut that will work; it has to be cleaned well. Before you re-assemble it make sure to use white lithium grease (high-temp grease) and grease all bearings. DrTom4444