I just spoke to my mechanic. I think what he did is lowered the transmission without lowering the skid plate by replacing a block that supports the transmission with a smaller one.
The four transmission bolts were not loosened, they dropped through the skid plate because the transmission was lowered.
Regardless, the transmission is vibrating and when the nuts are loosened it wiggles a bit and I can feel it. When the nuts are tight, it wants to wiggle but can't so the energy is transfered to the stick.
He is stopping over tomorrow.