Noises & vib feeling in truck

A few months ago, I've noticed a woop type noise and vib feeling in the drivers side floor and gas pedal. You can also feel it somewhat on the passanger side. I haven't been able to pinpoint it down and it's driving me nuts. I've made sure everything is tight and have greased the driveshaft. I even bought new tires which I really needed but it's still there. Just in the past few weeks / days, I 've noticed when I back out of my driveway and am turning the truck to the left, I'll get some strange noise and feeling that I can't describe. And just in the past few days, I've noticed that when I'm going around a corner (today it was turning left) I'll get a noise like something is shifting or moving around just like having something in your truck bed. Can't find anything wrong. (

Any suggestions. I don't want it to get any worse and don't really have to take it in somewhere.

 

I'm having almost the same problem and it started last night on my drive home from work. It sounds like a continual clunking noise under the truck but it sounds as though there is something lose in the bed. However, after driving slowly and getting it home safely, I felt it more in the floor boards of the truck and it started to sway from side to side as I was driving. It sounds like loud tires at first, I thought maybe i had a flat but then it sounded like the driveshaft had maybe come lose or something. I'm unsure as to what the problem is and nervous as to the cost to fix it lol. If you have any luck with the problem please share the information and I will do the same.