Refinancing an auto loan - in-house?

A year ago, my husband and I got an auto loan in both of our names. It was for $8000 and, while the payments are only $223, the interest rate is 18% and it’s a 60-month loan. This is because he didn’t have a beacon score at the time and we both had extremely limited credit.

This loan is through Wells Fargo and we’d like to keep it there because we’ve been happy with them and our new mortgage is with them (3.75%). In the past year we’ve paid the loan on time and built our credit considerably, enough to get mortgage anyways, so we’re wondering if we should go to the bank and see if they can refinance it at a lower rate.

I know we we won’t be able to get a 4% rate or anything, because our credit isn’t 720+, but anything would help. What, if any, ramifications are there related to refinancing an auto loan? What would it do to our credit? Any advice is appreciated.