Rear diff issues/questions

[that09ranger]

hello, i have a 2009 ford ranger 2wd, 2.3L i4. when i hit the gas semi hard, i hear a grinding/slipping and a delayed acceleration. i was wondering if this would be a rear diff issue, or if anyone has experienced it and has some advice. feel free to ask questions if you have any. thanks

 

[pjtoledo]

crawl under and look for leaks at the pinion. jerk on the pinion to check for up/down/sideways movement.
it will have considerable rotational movement, that is normal.

transmission in neutral, jack one rear tire and rotate it slowly feeling for "spots" or grinding/noises

does it also happen when L is selected?
how about when you turn the OD off?