This sound like your machine is unbalanced,adding padding to the floor joists does not automatically balance the machine,even checking the machine with a level doesen't always mean the machine is level--the best way to check a machine is to stand in front of the machine,with both hands try to rock the machine from front to back and from side to side,if there is no movement from the machine it is level--but for instance if the machine tilts back and forth from left front to right rear when you push on the top with both hands--this mean that only three legs are touching the floor--you will need to adjust the left front leg so all four legs are firmly touching the floor.

I just had the same problem with my Roper Washing Machine. My contractor installed it but didn't remove the packaging material which stabilizes the drum during shipping. Roper Customer Service said that this could cause sever shaking. My contractor didn't read the instructions. I tilted the machine forward and saw a yellow plastic tab underneath which had been cut. I grabbed it and tugged and out came the foor-long pin that hold the drum in place during shipping. Now there is only a slight tolerable shake. Make sure to unplug your machine first. Good luck.