How to deal with interfering grandparents?

Hi,

I was wondering whether anyone can advise re my DH's parents -
grandparents to the baby girl I have just recently had. I find them
incredibly interfering - they keep offering unwanted advice like their
word is gospel, and seem to delight when I do something wrong. My DH
is always on the phone to them discussing problems with the baby, so
they probably think we cant handle caring for her ok. The baby is
absolutely happy and healthy and there are no real problems in my
opinion.
To make matters worse, they dont do anything with their lives other
than look after their other grandchild - almost as if this child were
their own. As a result, this child is the most spoiled kid ever. They
want to come and visit regularly, but when they do, the conversation
never goes anywhere other than children and childcare - which to be
frank is a little boring - especially over the course of a few hours.
I really dont want them taking over the care of my baby and so I am
not sure how to tactfully tell them to back off? It wouldn't be so
bad if I could enjoy their company as adult to adult, but this hasn't
been possible so far.
thanks