Pea sized lump on trapezius muscle, on shoulder/upper back not neck, hard, immobile and painless, feels like it's attached to the muscle, what is it??

Trigger point?: Could be a lymph node, an area of muscle fibers that contracted and formed a small mass (overuse or after trauma) and/or may represent a "knot" or trigger point that can respond to tissue massage. If not growing or and painless ok to observe;get it checked out if growing/painful or persists (to make sure it's not something serious like a malignant growth)