Cathar,
This is why people with inate ability go into mechanical engineering and guys with square heads and those little propeller-twirly hats become electrical engineers. I sincerely doubt you have deformed the silver appreciably, certainly not to the tune of 3.5°C. Alas this is likely the realm of itty bitty quantum things orders of magnitude beneath what can be seen and directly observed. You'll probably have as much luck correlating this with the ocean tides as anything.
The obvious course of action is to try duplicating the results. Mount and dismount that silver block dozens of times and look for patterns to emerge.
I place my bet on it being a fluke, and I'm not referring to the multimeter of choice.
