Someone suggested I shove a pool noodle between the table top and the shelf... I was at the Dollar Tree the other day and they still had pool noodles (a lot of them too) so I bought one... and am so glad I did! I shoved it in there and now I have no vibration at all
I gave that machine a good workout this morning and it was blissful sewing. I'm going to feel really really spoiled the next time I have to sew with my machine on top of the table (every 3 Saturdays when my guild gets together to sew) but wow, I'm so glad I did this!
Thank you everyone for your support and ideas. I knew that the quilting community would have an answer that I didn't think of... who would have thunk it? A pool noodle