Recently, I noticed a slight vibration in my truck. It's really more of a low frequency noise/rumble, but I can feel a vibration with it as well. I've been feeling it when driving on the highway, about 65 mph / 1700 rpm. It is not consistent, but I seem to hear/feel it more when going downhill (i.e. slightly coasting). It tends to get better going uphill. Again, it's not consistent, and I have not noticed any surface/condition that can bring this condition on. Even, when it does rumble/vibrate, it is so slight that I wonder if I am trying to hard to hear something when nothing is wrong.

The tires look OK (not cupped too bad) and they are 315/70 All-Terrains on H2 rims & about 35,000 miles on them. Should I check out the u-joint? Front bearings? How do I check? Will the noise get worse & give me some notice before failure? I drive about 200 miles twice a week and would hate to be stranded. BTW, my truck is a 6 spd, SWD, 4X4 quad cab.

 

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that is a good place to start. lift front tire off ground rotate tire, turn steering to right or left and listen to the joint should be smooth no noise; put a crow bar under and lift tire while watching ball joints, if you see movement of more than 1/8" (some say less)your ball joints are going. second check lift both rear tires off ground, block front tires properly for safety, put tranny in N rotate tires by hand and listen to drive shaft u-joints, making a creaking noise they are going bad. this is what I would do to start, others may better methods for you.