Pentair pump won't start-up

[cscannon]

I have a pentair dual speed whisperflo 1 hp pump that is on the fritz in a very weird way.

- If it starts up in high speed, the motor just buzzes and doesn't turn over.

- If I start it up in low speed, it runs fine.

- If I start it up in low speed, then switch it to high speed, it also seems to run though the pressure gauge on my filter is about 5 or 10 psi less than it has been in the past.

Can anyone guess what is going on? Can the motor be replaced separate from the pump?

Thanks for your help