well i'd hate to state the obvious but......

could be a mod
could be a new proggy u added recently
something new running in the background
bla bla bla

what's your system specs?

have you updated your version yet?

does it crap out on any other map?

is your multiplayer still working?

i hope i have helped somewhat... but i fear that i may have been totally useless.

you might have to wait until a super brain comes in