Originally Posted by
discussmith
No guarantees but you could try a couple things. First I would put a tee on the output and put your ball valve on one side and allow this output to dump right back into the sump well. Allow the other side of the tee to extend back into your aquarium like before. You can then slow the return by opening the valve and allowing more water from the pumps output to just dump into the sump well. This will not restrict the pumps output and possibly quiet any vibration. If there is still vibration you could possibly dampen it from transferring to the floor by placing foam pads (like mouse pads) under the sump. Your restricting of the output is the way you are supposed to slow a pump without damaging it so you should be ok. It may be however that it was causing this vibration which sounds to me like it is creating harmonics with the surrounding structure.