I'm not a fan of it because the material is soft and porous. Also, unless the sump and where you place it are acting as a sound board, it may not make that much difference.
If you pump is connected using soft PVC tubing, you can do a simple test. While it's running, lift the pump off the sump, just enough so it's not touching. If it is silent now, you need to work on the pump mounting. If your still getting noise, the source is someplace else.
Assuming it's the pump, first make sure it's working right and it's clean, even on the inside. A worn or damaged impeller can cause all sorts of problems.
If the pump checks out, and it likely will, your nest step is to isolate the pump from the sump. In other words you want to mount it in such a way that it doesn't touch the sump directly. One quick fix is to place a filter pad under the pump. It's not ideal, but may solve the noise issue.
My personal preference is to suspend the pump away from the sump. To do this, you use some very heavy nylon fish line or string, and hang the pump using it. You only need to get it just off the bottom. You might need to make something of a sling to mount the pump. If your sump is inside your stand, you can usually find or mount a cross piece to the stand and suspend the pump from that. If the sump is outside the stand, you can still mount something from the stand so you can suspend the pump. Think in terms of how some pendant lighting is suspended.
This method can even be used on an externally mounted pump, but you usually need to mount the pump to a base of some sort first.
Another alternative is you have lots of money is to just replace the pump. The newer DC controlled pumps usually come with rubber feet and are extremely quiet.