Entry level lenses are usually 3 element affairs...by all means borrow a better one, try it out, and I'll bet your problem will disappear. I've never been disappointed with my El Nikkor lenses (a 50mm, a 105mm and a just obtained 150mm).

The 35mm negatives are small enough that warping or popping in the carrier shouldn't be a factor. Glassless carriers work quite well. Look to the lens for a 'cure'.