没有负载时,没有震动.This shows the machine is balanced. I thought about it few time, just don't know why. I think you still can try few things before call a professional.
1) put only few small clothes in to see it still happens. If works fine. You put too much cloth in last time. I believe you may already try this. This could not be the reason.
2) If yours is a top loader, open the back. There may be a rubber belt link the motor and wash tank. If it is loose, the wash tank will works fine without load but the belt will slip under load. You may able to tight it by pull the motor position a little.
If yours is front loader, for most machines there is a concrete weight block under the machine to keep balance. You can check it to see if it is secured.