Usually I find it absolutely impossible to concentate on music and performing another activity simultaneously (I mean if I tried to walk down the street listening to an MP3 player I would just bump into things). Therefore I am usually unable to listen to ANY music and work at the same time! That said, I sometimes find that there are some tasks I find it OK to listen to a few tunes (in fact this can enhance the experience). This is usually the kind of task where the engineering work is completed and it's a matter of adding detail and finishing things off (e.g. detailing up a component or assembly, doing all the fiddly stuff to get things to fit etc. which are kinda like a puzzle rather than anything that requires intense concentration). Do you listen to music when you do mechanical design work? If so, during what tasks and what kind of music?