Eccentric Sheaves, Sheave Runout
Eccentric sheaves will generate strong 1X radial components, especially in the direction parallel to the belts. This condition is very common, and mimics imbalance. This can be checked by removing the belts and measuring again. 1X vibration of an eccentric sheave or a sheave with runout will usually also show up at the other sheave.

Eccentric Sheave