Mouselook lags my game

[big_ole_jpn]

I don't like to keyboard turn because I don't have Down's, but I get brief lag spikes regularly when mouselooking. My framerate is steady otherwise; it only happens when mouselooking. These spikes are short but cause me to rotate a random number of degrees and start running a completely random fucking direction, resulting in my death since typically I only forget about the issue when I am running frantically.

I've compensated by keyboard turning but that's really stupid. Anyone know what to do about this?