Turning on my amp

[KwanzaaLizard]

Whenever I turn on my amp, the speaker quickly "extends" once, making a dull thumping noise, and the clipping light flickers on once. I'm not sure if this is a common thing or if it's going to hurt my speaker/amp, so I figured it shouldn't hurt to ask. It's an NA-650 and I'm running it at 8 ohms into my Trace 15" cab, btw. Any insight would be much appreciated!

[Plstrns]

Sounds normal to me.

[Exploiter8]

I turn the master volume down before powering up, if I hadn't already had it that way from powering down.

X8