[ecomodded]

A wheel is probably out of balance

Also
Your alignment may be off but you could have worn front end parts, dried out rubber bushings and worn ball joints(they usually make a light knock noise when going over bumps) or other worn parts, tierod ends etc. etc.

I would not pay for a alignment until I inspected the front end for worn parts and rubber bushings , replace what it needs then take it for an alignment.