NAD 3155 Pops when turned off

Have my sons college setup ready to go. He has a set of B&W 685s, NAD 3155, Audinst MX1 and Emotiva speaker cables.
Each time you turn the NAD off you get a pop through the speakers. Volume level does not matter. We spent time cleaning all the rca inputs, power plugs, buttons/knobs with deoxit and deoxit gold. That did take care of a cracking in the left channel when the volume knob was adjusted.

Is there a solution to the pop when powered off? Or is this normal with these older NADs?
Thanks in advance for your help.
That's normal for older NADs. Have to just live with it. Just make sure the volume control is at 0 and should not pose any problems for the speakers.
Meiwan is correct. Turn down the volume.
Thanks guys for your responses. Appreciate the help.
My old Sansui did the same thing. I placed a couple high wattage resistors in the second set of speaker outs (B). My speakers are on "A". When I'm ready to turn it off, I lower the volume, switch to the "B" speakers that have the resistors and turn it off. The resistors take the load. No pop. When I'm ready to listen again, I switch it to the "A" system and I'm set.
If you do this, be sure the resistors do not contact anything to short out. Place something on the leads if you need to.
Why turn it off .
Turn off pop could be the result of some excessive DC offset appearing at the output(s). The DC could be high enough to cause nuisance pops but not great enough to trigger the protection circuitry. This can occur in older amps as parts age and values drift. If the amp has offset trimpots, these can be adjusted to zero out the DC.