I have had this kick from the rear for a while now. it occurs in the morning after I've let the car warm up for 10-15 minutes. on the first 5-15 minutes of driving first thing it has a a bit of a kick only while gas is applied. its small and started off subtle but it has gotten more noticeable. after the said time of driving it goes away and it doesn't happen much at all during the day.

the rear axle seals have been replaced and the fuel filter has been replaced. this is all that has been done to the rear.

in the front I've done an oil change, and timing belt kit. i need to replace the front axle's, replace some vacuum lines, change the valve cover gasket and cam chain tensioner gasket.

any ideas? also if the rear axle seals are replaced does the rear diff fluid need to be replaced? if not then I doubt the mechanic changed it and if they did not could that possibly cause the kick until it has warmed up?