Foghorn noise worse after replacing IAC valve

[expinoy]

Help pls, newbie here. I've always have a problem with foghorn noise but only in cold weather and would disappear after engine is warm, so it didn't really bother me that much since I live here in Arizona. Couple of days ago, I started the truck and the idling was out of whack. Decided to replace the IAC valve for now, but it didn't fix the idling but made the foghorn noise worse even on hot weather! Check engine light did not turn on. Drove it around for a while even on the freeway, foghorn noise still there. The noise would go away for a second when accelerating but comes back when decelerating and goes away again when it's below 1,000 rpm. I have a 1998 Expy XLT 2WD, 4.6 and 233,000 miles. Thanks, any help is appreciated.