Kemper Power Rack at a Gig Today Sounded Like a Motorcycle.

I am a bass player. I was using my Power Rack Profiler today at a gig with an SVT 8x10 cab. It was an outdoor gig and it was hot outside, although the stage as covered.

During soundcheck, everything sounded great. About a song into the set, it started making all kinds of static and then a loud fluttering sound like a motorcycle. I tried turning it down and it stopped for a few seconds then started back up. I thought maybe my wireless was messing up so I switched to a guitar cable. No difference.

I had no backup head and the gig was ruined for me. When I got home from the gig, I turned on the kemper without the cab and only headphones and it sounded fine.

Could it possibly be a bad speaker cable? I don't think it's a blown speaker because the noise was coming from all of the speakers.

Could it have overheated?

I can't plug it into the SVT cab at home to test it because it is loud as hell and the neighbors will call the cops.

I ordered a new speaker cable and will try it at this weekend's gig and will be bringing a backup head just in case.

Has anyone experienced a bad speaker cable? What would it sound like?

Thanks for your advice.