Adcom 545 MKII Amp...A "Pop "Sound

The problem can be caused by many things, but input differential transistors going out of mismatch is the most common, followed by fading resistors in the feedback and/or input impedance. Also a problem is an electrolytic capacitor in the feedback divider leaking or having a high ESR. 

You're a good tech @gs5556 ; that's pretty much what was replaced in my Nakamichi PA-7A MKII when it was making a popping noise when turned on.

Is there a way to quiet down this pop sound ?

Use a speaker switch, after turn on the amp wait 5 second then turn on the speakers.

Or

Keep the amp on 24/7.

If the popping sound comes from the speakers, then you are getting a DC transient from the amplifier. Yes, it can damage the speakers, depending on the voltage.

Disconnect the speakers, place DMM probes on the + and - terminals. Set it to read VDC. Turn on the amp and note the voltage (it will go by quickly). If it jumps to over a volt, it can cause problems. But leave the probes there for a few minutes. If the DC offset drops below 50 millivolts (or better yet to a few millivolts), that is the amp showing its age. What you can do is disconnect the positive speaker cable prior to a cold start and then connect it after five minutes or however long it takes for the voltage to drop.

The problem can be caused by many things, but input differential transistors going out of mismatch is the most common, followed by fading resistors in the feedback and/or input impedance. Also a problem is an electrolytic capacitor in the feedback divider leaking or having a high ESR. 

Questions : Can this sound hurt my speakers ?

....does anyone have this issue ?

.....Is there a way to quiet down this pop sound ?

which order are you turning the preamp and amp on?