I have the same issue with the Stern shaker in my Deadpool LE. Loud jackhammer noise, little to no shake. I think Stern shakers used to have the bolt across the top, not sure why they don't anymore. Opened it up to tighten the bolt and was unpleasantly surprised.
I am approaching it as a defective part and am having my distrib talk to Stern about it. If that goes nowhere I'll try your fix out, or just buy a PBL shaker and stick to those from now on. Although the last PBL motor I bought seemed to no longer be designed to offset the weights to reduce the shake (only one hole for the set screw). Not sure if that is a new trend.
Dear shaker motor sellers: Please have the bolt and the ability to offset the weights so owners can adjust to their preference. Thanks.