[ICOM] 746 noise

[yash at aol.com]

 Just started using the 746 after it had a long spell in the closet. I noticed Ever increasing birdie,howl, between 18130 and 18133,also Increasing as frequency goes up. Also at 18116 to 18121,the same. Pulled the antenna same thing but up a few hundred kc. Shorted the ant input, little change. I don't hear this at all on my flex or drake. Iam assuming its the 746 doing this. Has anyone ever run into this on the 746? Iam thinking of a bunch of things that could cause this ,but thought I would ask if any one else experienced this. and its solution.
thanks
dale wt4t