Garmin 430, weak Loc/VOR

A student recently installed a Garmin 430. It will not pick up a
nearby VOR on the ground, while his old 170B will. The needle comes
alive just after liftoff, but it does seem to have a lot of course
roughness.

His localizer also exhibits a lot of course roughness when far out on
the localizer, say, 15 miles. In visual conditions, I could see the
airport off to our left, but the needle was centered. Shortly
thereafter,the needle moved left and he corrected to what appeared to
be truly the extended centerline of the runway.

I'm not comfortable with this aircraft in IMC until I'm assured the
course guidance is rock solid. Any thoughts as to what might be
causing these indications?