Problem - HF "Chirping" Using Turntable

To make a long story short, my PS Audio 5.5 preamp, Hafler DH-500 power amp and Acoustat 1+1 speakers have been thoroughly checked out, and they appear to not be the source of the problem below.

I installed a new Audio-Technica MM cartridge and since then (but the above components are "new" too) when my phono section is engaged, at high volumes there is breakthrough of a very disconcerting high frequency chirping or oscillation. When I move my TT to my (lower quality) home theater setup, there is no such noise.

So, I figure either my Tt (a KAB Acoustics-modified to play 78 rpm - Technics SLBD-era belt-drive TT) or the AT cartidge is the source of this noise or it happens to exist at the location of my system and the cartidge is amplfying it.

Any thoughts? My line-level channels are fine - silent.