Caldera Spa popping/crackle noises

[dpeters]

Have a 2018 Caldera tahitian with sound system and subwoofer.  About 2-3 months ago started getting awful popping or crackling noises from the subwoofer.  Would start with just a few pops, then at times would continue for a hour.  All times of the day/night.  We did have a handrail installed screwed into the frame of the spa.  And seems to have started after this was done.  Have had spa techs out 3 times and can not find what is causing the noises. 
This past week have removed the handrail and now we are just hearing a single or double popping noise roughly every 10 minutes. The constant noise has stopped with handrail off.
I do have audio of the sounds    Also do see there was a leak over one of the pumps caused rust buildup , and also the bottom of the heater looks rusty
Has anyone ever had this issue?

[Hottubguy]

Is the music system on or off when you are in tub?

[dpeters]

The ‘noises’ occur when we are not in hot tub.  Can be in the house. And hear it

[dpeters]

Here is a 30 second video with the noises   With the handrail on

https://youtu.be/7hY_93ZK63U

[CanadianSpaTech]

Is there an on/off switch inside the stereo enclosure? most subs will have a volume control built in that can be turned down a bit. https://manualzz.com/doc/29173345/stb-bluetooth-subwoofer-pairing-instructions
 
WITH NO MUSIC OR SOUNDS PLAYING, SYSTEM MAY       EXHIBIT LOW LEVEL BACKGROUND NOISE DUE TO        BT SEARCH FUNCTION.   TURN THE POWER SWITCH       “OFF” WHEN NOT IN USE.

[dpeters]

There is a Bluetooth on/off on the display and yes it is off.