08 GT 226,000 miles. The original alternator finally crapped out and I replaced it with a low mileage one from a junk yard. Ever since I replaced it, the fuel injectors have become extremely noisy. Is there a connection here or mere coincidence?

 

I don't think there is a connection, I think the coincidence is the 226,000 miles.
If you are comfortable doing it, I would say remove and clean them, lots of how to vids on youtube.

 

I really can't say if it has any bearing what so ever on a Mustang's injectors, I do have an '05 GT that still just sings like new at all of 76k miles. However,

I've been a believer of running fuel cleaners for a very long time, and at 69 years of age, that is sadly a very long time. Meanwhile I have used my last car, a '78 BMW as an illustration many a time. Sold it in 2007 with 269k on the engine. I had been modified at 132k pretty thoroughly, but the injectors were kept, except one. The other were still hanging around at 269k, also when that was done, I had a 5th injector installed for additional fuel flow when needed, never had a problem with that injector.

A "clincher" is that the BMW had clear, see through fuel lines from the fuel distributor to the individual injectors. Over the years I was in the BMW game I saw many a car with similar fuel lines no longer "see through" at 269k my fuel lines were STILL see through. Over the years I used what I thought was the "right one" many times. The "right one" did change, but didn't have any that I thought "whoops!" Right now I think the "right one" is Lucas Fuel Injector Cleaner. I can tell you for sure, when I add that to my GT's fuel, for my Yamaha FJR1300 with a "Power Commander" in charge they both seem to really HAPPY! :-) I don't run these cleaners in every tank, I run them on occasion, and if the "occasion" seems to be after too long, I give them a heavier dose. FYI FWIW

 

+1 for the Lucas Fuel Injector Cleaner. I use them once a year in my car, truck and motorcycle along with E0 fuel in all three. My daughter turned me on to Lucas as her husband and inlaws stated it was the best available and I had nothing to loose. Glad to see another seasoned gent posting here - I'm just a few years behind you (59). First car was a 1966 Ford Fairlane (moderately modified and excellent training vehicle!) purchased in 1972 in my junior year of HS.

 

So I gather you old farts don't think that all FI cleaners are same or at least similar? I kind of thought that as long as you use something decent that would be much better than nothing. Based on your recommendation I'll use Lucas cleaner next time. Is there anything special on the label or just FI cleaner? (I'm an old fart too - but never too old to learn something new LOL)