The market always takes a dip when they announce rate hikes. I'm not quite sure why, though.
Interest rate sensitive securities drive that.
For example, let's look at a perpetual preferred 6% ($100 par) share. The theoretical value is the dividend divided by your discount rate. Given that a preferred isn't a riskless security like a Treasury, we need to add a spread to the risk free rate. So the 10 Year US Treasury currently yields 1.85%. Let's add an arbitrary 300 basis point spread for a risk premium. So 6/0.0485=$123.71 (theoretical value, not what it is actually trading at). Now, let's imagine that the Fed hikes rates by 1% and the 10 year goes to 2.85%. Keeping the same spread, that preferred's theoretical value is now 6/0.0585=$102.56.
REITs, preferreds, some dividend payers are extremely sensitive to interest rate changes.
Fixed income buyers also get hit as yields and prices are inversely related.