Also, if you want to hand do it, I can step you through the systematics.
Rename your addons dir, and see if it still happens... if so, then it isn't in the addons directory and so you need to check the main entity directory.
However, if the spewer does stop, then you know it must be in the addons dir. Now, return the addons to working order, and once you're sure they'll work like they once did, move the racetank entities out in whatever fashion you can manage. Do this first to see if it's simply that the racetanks are being modified and referring to a spewer proper. If you do get rid of the problem, then you need to go through and find the offending racetanks and look at their explosion entities. From there, it's a straightforward process of elimination.
However, if removing the racetanks doesn't help, then you have a more sophisticated issue. This prolly calls for going through explosphere and explo and streamer entities and systematically eliminating them until the problem stops. The good news is that if you find the explosion entity that's specifically causing the problem, you'll have no more work to do... simply mod it to do what you want, and continue about your gaming business.
Hope this helps... if you're more of a hardcore kinda guy and like doing this stuff (I admit, I sorta have fun doing mysteries and hide n seek... I'm weird that way, hence my major is Computer Science in college right now).