Loud Pump Noise?

Hello everyone
I have 27' AG round pool and it is my 4th summer with it. The water is clear, pump is working, but today when I was finished vacuuming, the pump starting making a loud buzz noise (constant) and continued. I turned it off for a little while, checked the filter, all clear, pressure is reading ok on gage when it is running, but it is really loud now. Is this a sign that the pump is on its way out? God I hope not! It has been running 24/7 for the last week but last year I also ran it pretty well 24/7 and it didn't make any noise.
I'm assuming since it is running, and pressure is ok, water is circulating it should be ok, but I can't understand why it all of the sudden got so loud.
I turned it off for now and will leave it shut off for a couple of hours, but I thought I would ask if anyone else had a similar thing happen and if so did you eventually have to get a new pump?
Any suggestions would be appreciated.
Thanks
Mary

It could be one of a few of things:
1. impeller is loose - check for play of impeller
2. bearing going bad
3. Something inside pump chamber - check for a pebble or something similar

There is a duplicate thread located here:

http://www.poolforum.com/pf2/showthread.php?t=7572'

so I'm locking this one.
Al