Almost two years ago now, my pump started to get louder and the pitch kind of waivered up and down a little.... not a constant tone. Well, of course it died on me while I was out of town. Riding down the road, all of the sudden the car starts slowing down. I pull over on the side of the road and it dies. When I would turn the key, no more priming sound. I knew right away it was the pump. I did not have a cell phone yet at the time (got one the next day) and it was on a country road, so I had to walk about three miles to someone's house, ask to use their phone, call to my town and arrange a tow, etc, etc. It was not a fun experience.
The next day I got a generic auto-store pump and installed it. It lasted about a month then started giving me problems. I ordered a
BBK 190lph pump and it's been fine since.
By the way, most of the aftermarket pumps are made by Walbro. My BBK one has Walbro stamped on the side of it and a friend of mine's Holley pump does too.
If you already have the BBK pump, I'd go ahead and install it as soon as possible. These things don't give you any warning, they just die. And no fuel = no go. In my experience and most Mustang friends I've talked to, the pump getting louder or sounding different or weird usually means it's getting tired.
Hope this helps.