it's the high frequency in the tig causing it. it will cause all sorts of issues with electronics. I had a customer whose burning table would sporadically move by itself when the tig was being used. Both on separate circuits but the conduit that housed to wiring for the tig crossed over and was touching the conduit for the burning table. placed a piece of rubber between them and problem went away. You may try moving the ipod setup further away from the tig. (also keep your cell phone away from it when using the tig)