Throbbing in Rear

[sarahsdaddy]

I just got a good deal on a 2000 XLT AWD v6 SOHC, but there is an odd noise toward the rear, kind of a throbbing sound, seems more toward the right side. I took a chance on it since the vehicle was otherwise in super condition for the age. I can safely eliminate tire/wheel/bearing causes as it only happens when on the gas, but if I lift off it immediately disappears. It also seems to quiet down toward highway speeds. There is no other evidence of any tranny related problems. The previous owner said it had been doing that for years and two different mechanics could not figure it out. I figure (based on my limited newbie knowledge of Explorers) that anything in the rear can't be too awful expensive to replace. Any ideas?

 

[35Remmy]

"Throbbing in the rear" is never a good thing, pardon the pun. What is a throbbing sound? Like a pulsating? Are your tires wearing correctly?

 

[sarahsdaddy]

If you want to call it pulsing, a fairly rapid sound that varies with speed, kind of like you get with a wheel bearing going bad. The tires are nearly new and the problem apparently preceded them from what the seller said. There are no observable wear problems, it tracks well, brakes straight if you slam them with no hands on the wheel. I'm not sure what else. Something unbalanced in the rear drivetrain?

 

[jhclance]

Pinion bearing or a broken tooth in the rearend