KB9YZL,
The Peltier Effect does produce a constant voltage. Even independently of temperature. However, I think Thermocouples operate via this effect, so the voltage may be more as the temperature increases. But you will get a small voltage at any rate. As WB6BYU said, the corrosion factor is probably the worst aspect of it. However, this kind of voltage might just cause problems with noise as well, especially if the joint became loose and it started to move around and cause an oscillation. But the voltage is small in milliamps at best. But this might mess up an antenna mounted pre-amp or something like that. Copper and Aluminum are both good conductors, so the problem might be noticeable.
73
frank
KG4VLQ