I have a strange problem with the following setup:

Outlaw 1050/750 Combo
Parasound HCA-1500A driving a pair of Sonus Faber Concertos for the front channels.
I am driving the center channel (Sonus Faber Solo), the rears and the center surround with the 750. The center channel is a Sonus Faber Solo, which I want to bi-amp using two channels on the 750.

I removed the shorting bars on the speaker and connected the Center channel preamp out to two channels of the 750 with a Y connector.

I wired the two channels to the high and low connectors on the speaker. Everything sounds great.

About 15 seconds after I power off the amplifier, I hear a high pitched whine that descends in pitch for about 5 seconds from the tweeter in the center channel.

I know this is coming from the 750 because I hear it even when I disconnect the preamp inputs from the amp.

When I replace the shorting bars and connect the speaker conventionally with one pair of wire from one amp channel the sound disappears.

When I remove the bars and bi-wire from a single channel on the amp, there is no problem.

When I amp the tweeter from the center speaker terminals on the 1050 and the bass from a single channel on the 750, there is no problem.

Any assistance would be greatly appreciated!

Thanks,
Tony.