Problem with H/K Receiver

[Cool Mr Steve]

I currently have a Harmon Kardon AVR 340 and a pair of Swans 5.2 main speakers. I'm about to get a center channel for my system and build a set of surrounds, but I have an issue; When I "enable" the use of a center channel on my receiver the sound "oscillates," like there is a short in the system somewhere. The oscillation doesn't have any rhythm, the sound gets lower, then returns to normal whenever it feels like it. The receiver works perfectly when I use it in stereo mode, but when I enable the center channel, which I don't have but will be getting soon, the problem starts. I am about to take it to a repair shop to have it looked at (the fans don't work on it, either) but I wanted to know if anyone has any input.

*EDIT* I hooked up a crappy boom box speaker to the center channel output and enabled the center channel. Everything sounded correct and I wasn't able to pick up on the oscillation in my main speakers. Do I simply need a center channel hooked up when I enable it or it will sound incorrect?

[slayer]

That is the sound panning between the LCR's. When you had it hooked up without the center the info was just getting lost. Leave it on stereo until you get your center.

[Azeke]

Indeed, check you menu for your speaker mode configuration and try using the EzSet function when you have the set completed.

Peace and blessings,

Azeke

[Cool Mr Steve]

Exactly what I wanted to hear! Thanks a lot, guys!

[Cool Mr Steve]

Oops, posted twice... Thanks again!