Loud clunking when pump turns on

When our well pump turns on, the pipe that goes into the bladder pressure tank clunks loud enough to hear it throughout the house and at the same time the pipes rattle hard. We've drained the tank and the pressure is according to the manufacturer's recommendations. What's the problem?

You didn't mention what type of pump you have; jet or submersible or, if there is a check valve on the inlet of the pressure tank...

So, probably a stuck closed or binding check valve or a leak allowing some air into and some water out of a leak (above the water level in the well) and it and then water is slamming into a check valve or a loose stop valve washer somewhere in the plumbing past the pressure tank.