Today I came into the theatre at 2 PM after my classes for my schedualed crew hours. I noticed a faint "burning rubbery" smell, but we had been cutting PVC so I dismissed it, however not till after checking the booms where there were many cables close to the lights..nothing there. As the hours went by, a few people came into the theatre and commented it smelled odd...again the PCV explanation. Finally, around 4:45, one of the head techs went up to the catwalk to turn on the intels. We found the source of our problems. For some reason, all the S4's on the fourth catwalk were running very very hot. Even the pipe railing they were all hanging on was toasty. On the pipe is about twenty or so 575 watt Source 4's. These had been on, not even at full, since probably 9 ar 10 AM. What gets me is that we do this on a nearly daily basis, and this is the first time something like this has happened.