Noisy Mecaplex Window

The Mecaplex sliding window on my ASW 24 emits a loud whistle while in
the closed position, at all airspeeds.
The noise can be made to go away if I press firmly outward at the
trailing edge of the sliding window.

After a while it is so bothersome as to give me a headache. I have
tried stuffing a piece of paper towel in between canopy and window and
this will quiet the noise for the rest of the flight.

Note this canopy is a replacement, not original equipment.

Any ideas for a permanent fix would be appreciated.

Dan Fitzgerald