Both my trucks alternators are showing the voltage of leaking AC to be too high, around .29 V ac. Is there such a thing as a filter to filter out the AC noise?

Yeah replace the diodes. That's what filters out the noise and the diodes are just wore out or poor quality. You might be able to get just the diodes from alternator shop and do it yourself.Also you might double check with a high quality meter if you don't have one. Fluke or similar should be accurate. A good alternator like my two truck got are between 0.02 and 0.03 Volts AC.

Mike does this mean when buying a new alternator you have to test it before buying? :think:One last question.... How difficult is it to change the diodes yourself?

Just because the alternator is new or even rebuilt I always suggest bench testing before you leave the store. Sure it bad o go through all the trouble and get it installed to find another bad diode. It just best to test before you leave the store.Split the case in half and the diodes are typically just bolted to the rear case. Few screws and wires and change yourself if you can buy the diodes. When I was a pup I use to rebuild the 73 Dodge Charger alternator myself because brushes where about 10-12 bucks and diodes where like 20 bucks. Cheaper than 110 for a new alternator.