Why did Jefferson and Madison oppose the national bank?

They opposed government interference in the economy.

For the same reason Ron Paul and the Constitution Party opposes the Federal Reserve system.

It's a privately run corporation which makes phenomenal profits off of new currency being put into circulation (whether actually printed or just a digit in a computer) - that's pure inflation by the way - and whose owners have a vested interest in the government spending itself into debt (federal, states, counties, cities, towns, school districts, etc) and whose owners also make extra earnings from going to war (which explains why B.O. has failed to bring our troops home from Iraq).

Because a central bank that controls all the wealth in the nation. Can deflate and inflate the currency at their own accord. This would undermine the people and strip them of their wealth and liberties.

example~ if you have a savings account this year, and you have 1000 dollars in it, because of inflation your money will not have the same amount of spending power next year.

The federal reserve does the same thing, the government has no need to listen to the people because they have a printing press to pay for their program,s and wars, all at the expense of the poor who suffer the most from inflation.

The forefathers where aware of this and made it constitutional law to only have gold and silver as legal tender and made paper money illegal.

Section 10. No state shall enter into any treaty, alliance, or confederation; grant letters of marque and reprisal; coin money; emit bills of credit; make anything but gold and silver coin a tender in payment of debts; pass any bill of attainder, ex post facto law, or law impairing the obligation of contracts, or grant any title of nobility.