alternator or charging problem

2003 cvpi former FHP 81000 miles, bought there and drove 5000 miles to Seattle no problem. Car now has 87000 miles and when accelerated from dead stop to 70mph, the ampmeter dropped 50% and showed almost no charging. Cut all unnessecary power and drove home with no problem. Turned car off and it started right up, but had loose metallic sound under hood. Looked under hood and saw nothing unordinary. Shut off engine and inspected serpentine belt and found no problem. Inspected battery and suspect original ( 36 to 48 month motorcraft). Started car again and same noise. Day two drove car and ampmeter is reading normal ??, but same noise.
Need some suggestions, THANKS

Check the tensioner. It may be getting weak and allowing the belt to slip just a little and not allow the alternator to properly charge the battery. You may as well change both the pulleys while you are there also.

I had the same problem with the same car and found the alt was over charging and killed the battery. The gauge would go down like it was not charging and the lights would flicker. The car always started up though. I replaced both alt and batt and all has been fine.

These cars have been know for faulty regulaters which are in the altenator.

Good luck!

Thanks for the info. I'm starting to suspect that there maybe issue with the serpentine belt, but first I will take the car down to an auto parts store I go to and they will test the battery for free. I do not believe that the battery is the culprit, but it is at least 5 years old now and should be replaced. When I bought the car from the business in Florida, they had told me that the serpentine belt had been inspected and may have been replaced. Accelerating from a dead stop even though I did not burn rubber in it, could cause the serpentine belt to slip on the pulleys and create a low charging issue on the amp gauge. I started the car up Monday and no trouble. Amp gauge shows normal charge and there is no slippage on the belt and the battery light does not come on. I have a side question for you guys. When I bought the car and drove it back to Seattle, before I left Florida the Owner of the business showed some of the paperwork for the car from the FHP and said it belonged to a supervisor and Ford had reprogrammed the PCM in it. Does this add additional power ?? The thing sure hauled A!! on the way home. Thanks for all your help too.