Power Amp shut down sound thru R speaker ??

Hello.

I own a Levinson 23.5 power amp. In the past month I notice a low thump/distortion sound coming from the right channel/speaker when turning the power amp off.

To clarify it is only when the power amp is turned off. Then about a second later I hear a low thump/distortion sound coming from the right channel speaker (only the right channel speaker). It only lasts a split second and is very low.

The Power Amplifier is always first to power down. I have my preamp and source gear in a line conditioner. Always have the volume on the preamp all the way down when shutting down the power amp.

Should I worry or is it normal? Live with it?
Could it be fuses or is it definitely the power amp.
Trying to trouble shoot before paying the piper.

Thank you very much for your help.
joe