Newbie: Refinancing Duplex - find best rates

[Yu Liu]

I have been looking into refinancing an investment property (duplex) and have been given very mediocre rates. Currently my best one is 4%, 0 points, and $1500 towards closing costs. I was wondering what banks, credit unions, lenders other people are using as well as websites for me to get the best rates and lower my monthly costs.  What other things might I need to consider?

Location: Bronx NYC 

Property type: Duplex, investment

Loan still owed: $400,000 loan

Property worth: $700,000

Type of Loan: Regular refinance (not Cash out refinance)