Anybody have any idea what this could be...?

[photodisco]

Couple of weeks ago - while driving to the beach on vacation i noticed that on the hwy going about 70mph, if i got off the throttle and got back on it the truck would have a very slight vibration coming from the rear area and make a fairly audible resonating pulsating sound...it would do it almost everytime i tried on the 300 mile trip.

Recently (it's my wife's daily driver) after not driving it for a while, i could get it to do the same exact thing BUT it would not do it everytime i tried...only about 2/5 times or so.

There is also a distinct sound always coming in and it sounds almost as water does at a distance when it is boiling....this sound is constant and while the truck and it's horrible Goodyear tires do make a lot of noise i don't think this is related to the tires...could it be related to the driveline vibration?

Any thoughts would be appreciated...

 

[Houm_WA]

I don't know about the boiling sound but the vibration certainly could be the crap tires. I would at least visually check them for cupping on the inside to rule it out.