Mark Levinson 433 Pop sound

Hi,

I hope somebody can help me on this.

Just get a ML 433 and I noticed a pop sound when I turn on and off the unit (from standby to on). Pretty loud pop from all channels.

If I disconnect all the RCA inputs (with speakers connected), the pop sound disappears.

I did try two pre-amp and still have the same issue. Both of them are un-balanced preamp (Marantz and Conrad Johnson)

A couple questions with this:

1. Would using a balance Pre-amp and XLR connection solve this/minimize the pop sound?

2. How critical the xlr shorting pins to the pop sound?

3. Do you think there is something wrong with the 433?

This is actually the second units, the first unit did the same pop sounds. But it was also have humming/ground loop issues. It finally stop working after about a month of use. I'm just worry if the second unit have the same issue as the first, and would stop working as well.

Thanks