Might have been due to the length

I can certainly hear the IS in my 55-250 lens working where as i cant hear it in my 18-55 lens, cant feel it though.

Yeah, I can hear it working as a high pitch electric noise, but other than that you wouldnt know it was on. The Tamron lens in question wasnt connected to a camera or extended out or anything. I only opened the box as when I picked it up to start with I thought it must be broken so I decided to check it to see.