How do you differentiate between an out of balance wheel or a tire that has a blister/bump.

-Rob K.

could underflation cause a noise or vibration?

My experience is that underinflation accentuates the symptoms produced by a tire that has ply separation under the tread (tread face bulges). Over inflation will often accentuate the symptoms produced by a tire that has the sidewalls scuffed too thin (side bulges). Underinflation by itself (at least down to about 20 psi) should not produce any noticeable problems other than mushy handling and a slight pull to one side. Check that the rim is not contributing to the problem, like damage from potholes or curbs. Raise the car and spin the rim against a fixed reference point marker (like a washable felt pen held on top of a wood box) to check the side and under faces outside the rim sill where the tire bead seats. Check inside and outside of the rim. Rims are more susceptible to pot hole damage with low tire inflation. Alloy rims are also more susceptible to damage with low profile tires.
--
Dave -not to be confused with a real expert, just goofing around at this

Take a read of this thread from the archives
--
Dave -not to be confused with a real expert, just goofing around at this

The best way I can think of(other than jacking the vehicle and spinning the wheels, and visually inspecting them) is to drive very slowly, and the car will have a rocking motion as it rolls over the spot on the tire where the 'bump' is. Another indicator is if it is a balance issue, you will usually have the shake or shimmy reoccurring at the same speed, and when you get to a point faster (or slower aometimes) than that it will sometimes smooth out.

A warped wheel is another issue ... could it be that?

Hope I helped;
randyb