Why does my Heavy whipping cream pound cake have an aftertaste between flour and metallic?

All of my dry and wet ingredients were perfectly measured and at room temperature. I did not use baking powder as the recipe did not require it. I substituted vanilla extract (McCormick) for vanilla flavoring (McCormick). I baked the cake in the oven on 325 in a pre-heated oven for 90 minutes, let it cool for 20 minutes, and then removed it from the baking pan and onto a cooling rack for 3 hours. Otherwise the cake baked perfectly and was delicious until I finished the first slice.

The recipe was as follows:

Ingredients

• 1 ½ cups (3 sticks) of salted butter, softened
• 3 cups of white granulated sugar
• 6 large eggs (room temp.)
• 3 cups of sifted Swans Down Cake Flour
• ½ tsp of vanilla extract
• ½ pint of Heavy Whipping Cream
• 2 cups of sifted powdered sugar
• ¼ cup (½ stick) of butter, melted
• 2–4 Tbsp of heavy cream
• Extract/flavoring, if desired

Steps:

1. Preheat oven to 325°F.
2. In large mixing bowl, cream butter then gradually add sugar beating on medium speed until creamy.
3. Add eggs, one at a time, beating just until blended after each addition.
4. Add Swans Down Cake Flour and heavy whipping cream alternately beating on low speed until just blended as over beating will yield a dry and heavy cake.
5. Add vanilla; for richer flavor, add additional 1 ½ tsp. vanilla extract.
6. Pour into prepared pan
7. Bake 90 minutes