MMC workqueue kernel thread. Sometime around 2.6.18 they changed API for starting kernel threads. Once MMC code started to use new API, priority of mmcqd 'automagically' raised from 0 to -5. I'm not sure if it is bug or feature. -5 is above most important system daemons including osso-media-server. IMO lowering it back to 0 should not do any harm, there should be no time critical code that needs higher priority in there.

New mmcqd thread is started for each slot when card is inserted and it stops when card is removed. I don't think the stutter is related to 24 vs 48MHz bus speed but never verified this theory. It happens more often when booting from card due to higher MMC I/O traffic overall.