Rear-end Vibration under load from 1500-2500rpm?

[HokieDSM]

I've been trying to conserve gas a little lately, so I've been keeping under 3500rpm when I'm driving around usually. I've noticed that if I'm cruising in, say - 3rd gear, under 3000rpm - if I step on the gas to accelerate, I get a vibration feeling from underneath the car, towards the rear. Anyone know what could cause this? I've been meaning to do an oil change for the rear end, would that help?

 

[xcelr8n]

my car does exact same thing man... check youre carrier bearings mine are shot yours are probably done to