Hanging page loads every n loads
Solution 1:
- Apache is throwing seg faults
There's your problem. Apache isn't hanging, your browser is hanging when apache's child dies and doesn't complete the request.
LogLevel debug may give you a bit more information (though, a ton of information if this is a busy production system).
My first guess would be suhosin/mod_security or something that is compiled against the wrong php api or possibly using shared libraries that have changed slightly. I'd doublecheck those and if you can isolate the different php extensions/apache modules that are running. Are you running apcc, eaccelerator or any opcode cache? Zend? Source Guardian? ioncube? Are you using the right version of each of these? Latest updates? Zend 3.3.9, ioncube had a recent update as well and can cause segfaults depending on the version of Zend you're running.
Solution 2:
Bind something like strace or gdb to all of the apache worker processes, and reload pages in the browser one breaks. Then you'll get to see more info about what it's doing when it's crashing.
When you say that you've enabled coredumps, did you also enable them to be large enough to handle an Apache coredump? It's likely to be fairly large, so even setting them to unlimited-size temporarily might help.